Recyclable polymers based on ring-fused gamma-butyrolactones

ABSTRACT

The invention discloses a class of new polymers, trans-ring-fused poly(4-hydroxybutyrate)s (RF-P4HB) that exhibit a unique set of properties, including robust thermal stability and mechanical strength, quantitative recyclability to the building block monomers via thermolysis and/or chemical catalysis, and convenient production from the chemical ring-opening polymerization under ambient temperature and pressure. Another unique property is the formation of crystalline stereocomplexed polymers with high melting temperature upon mixing the two enantiomeric RF-P4HB chains via stereocomplexing co-crystallization. This invention also provides the corresponding ring-fused lactone monomer structures that enable the synthesis of the RF-P4HB polymers, through trans-fusing of rings to the parent γ-butyrolactone ring. Furthermore, a polymerization or copolymerization process for the synthesis of RF-P4HB polymers and copolymers is disclosed.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119(e) to U.S.Provisional Patent Application No. 62/540,672, filed Aug. 3, 2017, whichis incorporated herein by reference.

GOVERNMENT SUPPORT

This invention was made with government support under Grant No.NSF-1664915 awarded by the National Science Foundation. The governmenthas certain rights in the invention.

BACKGROUND OF THE INVENTION

Various approaches have been pursued to address the unsustainable annualgeneration and disposal of several hundred million metric tons ofsynthetic polymers, with the goal of a circular plastics economy. Theuse of renewable resources as feedstock materials generally does notaddress materials' end-of-use problems. The development of biodegradablepolymers for biological recycling also provides a partial solution butfails to recover valuable building block chemicals. Degraded materials,especially those that only partially degrade, can also cause unintendedenvironmental consequences. Mechanical reprocessing tends to degrade thequality of the polymers. In contrast, chemical recycling can allow forrecovery of the precursor building block chemicals via depolymerizationor creative reuse or repurposing through the generation of value-addedmaterials.

With specifically designed monomers, reaction conditions can be used toselect the direction of the monomer-polymer equilibrium or theclosed-loop chemical cycle, with low temperatures and bulk or highmonomer concentrations favoring polymerization and high temperatures ordilution triggering depolymerization. Several classes of recentlydesigned recyclable polymers operate under this thermodynamic principle,such as poly[2-(2-hydroxyethoxybenzoate)],poly(β-methyl-δ-valerolactone), and a polycarbonate (PC) derived fromcopolymerization of CO₂ with a meso-epoxide.Poly[2-(2-hydroxyethoxybenzoate)] exhibited relatively low glass (˜27°C.), melting (˜69° C.), and decomposition (˜146° C.) temperatures; thethermostability of the PC was also limited (below 260° C.), and itsdepolymerization underwent decarboxylation.

However, the chemical recycling approach still faces challenges,including the selectivity involved in chemical recycling processes andcircular monomer-polymer-monomer cycles, as well as trade-offs betweenpolymers' depolymerizability and properties. A notable example fordepolymerization selectivity is biodegradable poly(L-lactide) [P(L-LA)],which produces a mixture of many products upon thermolysis or a mixtureof LA stereoisomers and cyclic oligomers upon chemolysis with a tin (Sn)catalyst, thus requiring substantial separation and purification beforethe recovered L-LA can be reused. Polymers with a low ceilingtemperature (T_(c)) are readily depolymerizable under mild conditions,but they typically do not have robust enough physical and mechanicalproperties to be useful for most common applications. For example,poly(γ-butyrolactone) (PGBL), synthesized via catalyzed ring-openingpolymerization (ROP) of the renewable, non-strained, thermodynamicallyhighly stable five-membered γ-butyrolactone (GBL), can be selectivelyand quantitatively depolymerized back to GBL upon heating of the bulkmaterial at 260° or 300° C., depending on PGBL topology. However, thesynthesis of PGBL requires energy-intensive, industrially undesirablelow-temperature conditions (typically −40° C.), and PGBL exhibitslimited thermostability and crystallinity, with a low melting transitiontemperature (T_(m)) of ˜60° C. Another example of a completelyrecyclable polymer was produced through the chemoselective ROP ofbioderived a-methylene-y-butyrolactone; however, not only was a lowtemperature (−60° C.) required for the polymer synthesis, but theresulting polymer was also a noncrystalline amorphous material.

Furthermore, the ring-opening polymerization (ROP) of cyclic esters orlactones is currently the most effective route for the chemicalsynthesis of technologically important, biodegradable and/orbiocompatible aliphatic polyesters. However, this method is applicableonly to common 4-, 6-, and 7-membered lactones with relatively highstrain energy. The five-membered γ-butyrolactone (GBL) is a desirablemonomer for the chemical synthesis of the corresponding biopolymerpoly(γ-butyrolactone), PGBL, a structural equivalent of the microbialpoly(4-hydroxybutyrate) (P4HB), which has been shown to exhibit severaldesirable properties for biomedical applications. Noteworthy also arethe facts that GBL is a biomass-derived renewable monomer produced in alarge industrial scale and PGBL can be completely recyclable back to itsbuilding block monomer in quantitative yield by simply heating the bulkmaterial at 220° C. (for the linear PGBL) or 300° C. (for the cyclicPGBL) or in the presence of a catalyst at room temperature (Hong, M.;Chen, E. Y.−X. Nat. Chem. 2016, 8, 42-49). However, due to its lowstrain energy (i.e., high thermodynamic stability) of the five-memberedlactone ring, GBL can only be ring-open polymerized under extremeconditions, such as ultrahigh pressure (e.g., 20,000 atm), into lowmolecular weight oligomers. Using powerful molecular catalysts, the ROPof GBL can take place under ambient pressure, but it requires very lowtemperature and high monomer concentration conditions (below −40° C.),producing PGBL with limited molecular weight (M_(n) up to 30 kg/mol).Typically, polymers are required to possess sufficiently high molecularweight to render them sufficient physical integrity and mechanicalstrength to be practically useful.

Accordingly, there is a need to discover new GBL-based monomers that notonly can be polymerized under ambient conditions but can also lead tohigh molecular weight polyesters, while maintaining the chemicalrecyclability. Ideally, such monomers should be readily prepared fromcommercially available resources, can be polymerized under industriallyconvenient conditions (e.g., room temperature), and can produce thecorresponding polyesters with relatively high molecular weight(M_(n)>100 kg/mol) and chemical recyclability (depolymerization back tomonomer in high to quantitative selectivity).

SUMMARY

This disclosure provides a class of new ring-fusedpoly(4-hydroxybutyrate)s that exhibit robust thermal stability andmechanical strength, quantitative recyclability to the building blockmonomers via thermolysis and/or chemical catalysis, and convenientproduction from the chemical ring-opening polymerization under ambienttemperature and pressure.

Accordingly, this disclosure provides a polymer comprising Formula I,Formula II, or Formula III:

wherein

Q and R are the terminal ends of the polymer, or Q and R taken togetherform a cyclic polymer of Formula I, Formula II, or Formula III;

G is O, S, or NR^(z);

R^(x), R^(y) and R^(z) are each independently H or —(C₁-C₈)alkyl;

m is about 20 to about 10¹⁰; and

n is 1-20;

wherein the R^(y) substituents have a trans-configuration relative toeach other, each —(C₁-C₈)alkyl moiety is independently branched orunbranched, and each ring-embedded carbon independently has an optional—(C₁-C₈)alkyl substituent or phenyl substituent.

This disclosure also provides a method for polymerization comprisingcontacting a monomer with a catalyst and an optional protic initiator toform a polymer via ring opening polymerization reaction of the monomer,wherein the monomer is a monomer of Formula IV or Formula V:

or an enantiomer or mixture thereof, wherein

G¹ is —C(═O)— and G² is O, S, or NR^(z); or

G¹ is O, S, or NR^(z) and G² is —C(═O)—;

G³ is O, S, or NR^(z);

R^(x), R^(y) and R^(z) are each independently H or —(C₁-C₈)alkyl; and

n is 0-20;

wherein each —(C₁-C₈)alkyl moiety is independently branched orunbranched, and each ring-embedded carbon independently has an optional—(C₁-C₈)alkyl substituent or phenyl substituent.

This disclosure also provides novel polymers (or copolymers), such aspolymers of Formulas I-III, monomers and other intermediates for thesynthesis of polymers (or copolymers), such as Formulas I-III, as wellas methods of preparing polymers (or copolymers), such as FormulasI-III. The invention also provides polymers (or copolymers), such asFormulas I-III, that are useful as intermediates for the synthesis ofother useful polymers (or copolymers).

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings form part of the specification and are includedto further demonstrate certain embodiments or various aspects of theinvention. In some instances, embodiments of the invention can be bestunderstood by referring to the accompanying drawings in combination withthe detailed description presented herein. The description andaccompanying drawings may highlight a certain specific example, or acertain aspect of the invention. However, one skilled in the art willunderstand that portions of the example or aspect may be used incombination with other examples or aspects of the invention.

FIG. 1. Structures, intrinsic viscosity, and elution behavior. (A)Structures of the monomer, catalysts, and the resulting linear andcyclic polymers. RT, room temperature; t-Bu, tent-butyl; THF,tetrahydrofuran; ^(i)Pr, isopropyl. (B) Double-logarithm(Mark-Houwink-Sakurada) plots of intrinsic viscosity [η] versus absoluteM_(w) of linear (top) and cyclic (bottom) P(M1) produced by La1 with ROHand La1 alone, respectively. (C) Logarithm plots of M_(w) versus theelution volume of optically active linear and cyclic P[(R)-M1] producedby La1 with ROH and La1 alone, respectively.

FIG. 2. Thermostability and chemical recyclability of P(M1). (A) TGAcurves for c-P(M1) obtained with [M1]/[La1]=2000/1 (red) and l-P(M1)obtained with [M1]/[La1]/[Ph₂CHCH₂OH]=500/1/3 (blue) and a comparativeexample for the linear PGBL obtained with[GBL]/[La1]/[Ph₂CHCH₂OH]=400/1/3 (black). (B) Overlays of DTG curves forl-P(M1) obtained with Y1 (orange), P[(R)-M1] with Y1 (blue), P[(S)-M1]with Y1 (red), and a 1:1 P[(R)-M1]−P[(S)-M1] blend (green) and acomparative example for linear PGBL (black). (C) Overlays of ¹H NMRspectra (25° C., CDCl₃, with residual solvent peaks at 7.26 and 1.56 ppmfor CHCl₃ and H₂O, respectively): (a) c-P(M1); (b) the colorless liquidproduct recovered after depolymerization (toluene, 2 mol % ZnCl₂, 120°C., 24 hours); (c) clean-starting M1 for comparison.

FIG. 3. Thermal transitions and spectroscopic properties. (A) DSCfirst-heating-scan curves (10° C./min). (B) DSC second-heating-scancurves [5° C./min for (a) and (b) or 1° C./min for (c), after firstcooling at 10° C./min]. (C) Overlays of FTIR spectra in the carbonylstretching region. str, stretching frequency. (D) Powder XRD profiles.In all cases, 1-P(M1) polymers were prepared with [M1]/[Y1]=1000/1:l-P[(S)-M1] (a), l-P[(R)-M1] (b), and 1:1 l-P[(R)-M1]−l-P[(S)-M1] blendor sc-P(M1) (c).

FIG. 4. Mechanical and rheological properties. (A) Overlay of storagemodulus E′ and loss modulus E″ for sc-P(M1) measured by DMA (tensionfilm mode, 0.05% strain, 1 Hz, 3° C. min⁻¹). (B) Stress-strain curvesfor rac-P(M1) and sc-P(M1) measured by tensile testing (5.0 mm/min, roomtemperature, with the break point indicated by ×). (C) Rheology mastercurve (dynamic storage modulus G′ and loss modulus G″ versus angularfrequency ω) for rac-P(M1), reported as a time-temperature superpositioncurve at reference temperature 215° C. (D) Dynamic shear viscosity ofrac-P(M1) as a function of the shear rate measured at 215° C.

FIG. 5. ¹H NMR (CDCl₃, 25° C.) spectrum of P(3,4-T6GBL) obtained by[monomer]/[La[N(SiMe₃)₂]₃]=100/1, for a cyclic polymer (i.e., nodetection of end groups).

FIG. 6. MALDI-TOF spectrum of P(3,4-T6GBL) produced with a ratio of[monomer]/[La[N(SiMe₃)₂]₃]=100/1 and plot of m/z values (y) vs. thenumber of monomer repeat units (x), showing a cyclic polymer structure(i.e., no end groups).

FIG. 7. MALDI-TOF spectrum of P(3,4-T6GBL) produced with a ratio of[monomer]/[La[N(SiMe₃)₂]₃]/[Ph₂CHCH₂OH]=1000/1/3 and plot of m/z values(y) vs the number of monomer repeat units (x), showing a linear polymerstructure.

FIG. 8. DSC curves for P(3,4-T6GBL): (a) [M]/[La[N(SiMe₃)₂]₃]=100/1,T_(g)=51.6° C. for cyclic P(3,4-T6GBL); (b)[M]/[La[N(SiMe₃)₂]₃]/[Ph₂CHCH₂OH]=500/1/3, T_(g)=47.2° C. for linearP(3,4-T6GBL).

FIG. 9. Overlay of ¹H NMR spectra of P(3,4-T6GBL) obtained by (a)[(±)-3,4-T6GBL]/[La[N(SiMe₃)₂]₃]=2000/1; (b) [(R)-3,4-T6GBL]/[Y]=1000/1;and (c) [(S)-3,4-T6GBL]/[Y]=1000/1.

FIG. 10. Overlay of ¹³C NMR spectra of P(3,4-T6GBL) obtained by (a)[(±)-3,4-T6GBL]/[La[N(SiMe₃)₂]₃]=2000/1; (b) [(R)-3,4-T6GBL]/[Y]=1000/1;and (c) [(S)-3,4-T6GBL]/[Y]=1000/1.

FIG. 11. Overlays of TGA curves of linear P(3,4-T6GBL) obtained by (a)[(±)-3,4-T6GBL]/[Y]=1000/1 (slope far right), T_(d)=341.8° C.; (b)[(R)-3,4-T6GBL]/[Y]=1000/1 (slope far left), T_(d)=326.6° C.; and (c)[(S)-3,4-T6GBL]/[Y]=1000/1 (middle slope), T_(d)=323.2° C.

FIG. 12. Overlays of TGA curves of linear P(3,4-T6GBL) obtained by (a)[(±)-3,4-T6GBL]/[Y]=1000/1 (tallest peak), T_(max)=391.0° C.; (b)[(R)-3,4-T6GBL]/[Y]=1000/1 (middle peak), T_(max)=379.1° C.; and (c)[(S)-3,4-T6GBL]/[Y]=1000/1 (shortest peak), T_(max)=383.6° C.

FIG. 13. Thermal recyclability of linear P(3,4-T6GBL). ¹H NMR spectra(CDCl₃): bottom, linear P(3,4-T6GBL) prepared from the ROP with[3,4-T6GBL]/[La[N(SiMe₃)₂]₃]/[Ph₂CHCH₂OH]=1000/1/3; middle, thecolorless liquid product obtained after thermal degradation at 300° C.for 1 h; top, 3,4-T6GBL monomer for comparison.

FIG. 14. Thermal recyclability of cyclic P(3,4-T6GBL). ¹H NMR spectra(CDCl₃): bottom, cyclic P(3,4-T6GBL) prepared from the ROP with3,4-T6GBL/La[N(SiMe₃)₂]₃=100/1; middle, the colorless liquid productobtained after thermal degradation at 300° C. for 24 h; top, 3,4-T6GBLmonomer for comparison.

FIG. 15. Chemical recyclability of linear P(3,4-T6GBL). ¹H NMR spectra(CDCl₃): bottom, linear P(3,4-T6GBL) prepared from the ROP with3,4-T6GBL/La[N(SiMe₃)₂]₃/Ph₂CHCH₂OH=1000/1/3; middle, the colorlessliquid product obtained after thermal degradation catalyzed by ZnCl₂ intoluene at 120° C. for 12 h; top, 3,4-T6GBL monomer for comparison.

FIG. 16. Chemical recyclability of cyclic P(3,4-T6GBL). ¹H NMR spectra(CDCl₃): bottom, linear P(3,4-T6GBL) prepared from the ROP with3,4-T6GBL/La[N(SiMe₃)₂]₃=100/1; middle, the colorless liquid productobtained after thermal degradation catalyzed by ZnCl₂ in toluene at 120°C. for 24 h; top, 3,4-T6GBL monomer for comparison.

FIG. 17. Overlays of TGA curves of linear P(M1)s obtained by Y1 (orange)with [(±)-M1]/[Y1]=2000/1, T_(d)=342° C.; P[(R)-M1] by Y1 (blue) with[(R)-M1]/[Y1]=1000/1, T_(d)=326° C.; P[(S)-M1] by Y1 (red) with[(S)-M1]/[Y1]=1000/1, T_(d)=323° C.; 1:1 P[(R)-M1]/P[(S)-M1] blend(green), T_(d)=344° C.; and comparative example of linear PGBL (black)with [GBL]/[La1]/[Ph₂CHCH₂OH]=400/1/3, T_(d)=201° C.

FIG. 18. DSC first heating scan curves for linear P(M1)s obtained by:(a) [(S)-M1]/[Y1]=1000/1, T_(m)=126° C., ΔH_(m)=28.1 J/g; (b)[(R)-M1]/[Y1]=1000/1, T_(m)=126° C., ΔH_(m)=32.5 J/g; (c) stoichiometricP[(R)-M1]/P[(S)-M1] blend, T_(m)=203° C., ΔH_(m)=53.0 J/g. All polymersamples were crystallized from CHCl₃. The first heating rate was 10°C./min and cooling rate was 10° C./min.

FIG. 19. DSC second heating scan curves for linear P(M1)s obtained by:(a) [(S)-M1]/[Y1]=1000/1; (b) [(R)-M1]/[Y1]=1000/1; (c) stoichiometricP[(R)-M1]/P[(S)-M1] blend, T_(c)=108° C., T_(m)=188° C., ΔH_(m)=25.2J/g. All polymer samples were crystallized from CHCl₃. The first heatingrate was 10° C./min and cooling rate was 10° C./min, and the secondheating rate was 5° C./min except for (c) (1° C./min).

FIG. 20. DSC first heating scan curves for cyclic P(M1)s obtained by:(a) [(S)-M1]/[La1]=500/1, T_(m)=127° C., ΔH_(m)=36.7 J/g; (b)[(R)-M1]/[La[La1]=500/1, T_(m)=127° C., ΔH_(m)=33.5 J/g; (c) astoichiometric blend of P[(R)-M1]/P[(S)-M1], T_(m)=198° C., ΔH_(m)=60.8J/g. All polymer samples were crystallized from CHCl₃. The first heatingrate was 10° C./min and cooling rate was 10° C./min.

FIG. 21. DSC second heating curves for cyclic P(M1)s obtained by: (a)[(S)-M1]/[La1]=500/1; (b) [(R)-M1]/[La[La1]=500/1; (c) a stoichiometricblend of P[(R)-M1]/P[(S)-M1], T_(c)=122° C., T_(m)=188° C., ΔH_(m)=36.3J/g. The second heating rate was 5° C./min.

FIG. 22. Overlay of storage modulus E′ and loss modulus E″ for rac-P(M1)measured by DMA (tension film mode, 0.05% strain, 1 Hz, 3° C. min⁻¹).

FIG. 23. Overlay of a representative curve of tan δ of amorphousrac-P(M1) and crystalline sc-P(M1) determined by DMA.

DETAILED DESCRIPTION

Some polymers, such as polyethylene terephthalate in soft drink bottles,can be depolymerized back to the starting monomers. This makes itpossible to repolymerize true virgin material for repeated use.Described herein is a polymer based on a five-membered ring cyclicmonomer derived from y-butyrolactone that could be produced at ambienttemperature and mild conditions. The high-molecular-weight polymersexhibited high crystallinity and thermal stability. However, ateffectively hot conditions, or at lower temperatures in the presence ofa zinc chloride catalyst, the polymers could be returned to its startingmonomers and thus recycled into new material.

This disclosure provides ring-fused GBL monomer structures, theresulting RF-P4HB polymer structures, and catalysts/initiators used toproduce such polymer structures.

Definitions

The following definitions are included to provide a clear and consistentunderstanding of the specification and claims. As used herein, therecited terms have the following meanings. All other terms and phrasesused in this specification have their ordinary meanings as one of skillin the art would understand. Such ordinary meanings may be obtained byreference to technical dictionaries, such as Hawley's Condensed ChemicalDictionary 14^(th) Edition, by R. J. Lewis, John Wiley & Sons, New York,N.Y., 2001.

References in the specification to “one embodiment”, “an embodiment”,etc., indicate that the embodiment described may include a particularaspect, feature, structure, moiety, or characteristic, but not everyembodiment necessarily includes that aspect, feature, structure, moiety,or characteristic. Moreover, such phrases may, but do not necessarily,refer to the same embodiment referred to in other portions of thespecification. Further, when a particular aspect, feature, structure,moiety, or characteristic is described in connection with an embodiment,it is within the knowledge of one skilled in the art to affect orconnect such aspect, feature, structure, moiety, or characteristic withother embodiments, whether or not explicitly described.

The singular forms “a,” “an,” and “the” include plural reference unlessthe context clearly dictates otherwise. Thus, for example, a referenceto “a compound” includes a plurality of such compounds, so that acompound X includes a plurality of compounds X. It is further noted thatthe claims may be drafted to exclude any optional element. As such, thisstatement is intended to serve as antecedent basis for the use ofexclusive terminology, such as “solely,” “only,” and the like, inconnection with any element described herein, and/or the recitation ofclaim elements or use of “negative” limitations.

The term “and/or” means any one of the items, any combination of theitems, or all of the items with which this term is associated. Thephrases “one or more” and “at least one” are readily understood by oneof skill in the art, particularly when read in context of its usage. Forexample, the phrase can mean one, two, three, four, five, six, ten, 100,or any upper limit approximately 10, 100, or 1000 times higher than arecited lower limit.

As will be understood by the skilled artisan, all numbers, includingthose expressing quantities of ingredients, properties such as molecularweight, reaction conditions, and so forth, are approximations and areunderstood as being optionally modified in all instances by the term“about.” These values can vary depending upon the desired propertiessought to be obtained by those skilled in the art utilizing theteachings of the descriptions herein. It is also understood that suchvalues inherently contain variability necessarily resulting from thestandard deviations found in their respective testing measurements. Whenvalues are expressed as approximations, by use of the antecedent“about,” it will be understood that the particular value without themodifier “about” also forms a further aspect.

The terms “about” and “approximately” are used interchangeably. Bothterms can refer to a variation of±5%,±10%,±20%, or±25% of the valuespecified. For example, “about 50” percent can in some embodiments carrya variation from 45 to 55 percent, or as otherwise defined by aparticular claim. For integer ranges, the term “about” can include oneor two integers greater than and/or less than a recited integer at eachend of the range. Unless indicated otherwise herein, the terms “about”and “approximately” are intended to include values, e.g., weightpercentages, proximate to the recited range that are equivalent in termsof the functionality of the individual ingredient, composition, orembodiment. The terms “about” and “approximately” can also modify theend-points of a recited range as discussed above in this paragraph.

As will be understood by one skilled in the art, for any and allpurposes, particularly in terms of providing a written description, allranges recited herein also encompass any and all possible sub-ranges andcombinations of sub-ranges thereof, as well as the individual valuesmaking up the range, particularly integer values. It is thereforeunderstood that each unit between two particular units are alsodisclosed. For example, if 10 to 15 is disclosed, then 11, 12, 13, and14 are also disclosed, individually, and as part of a range. A recitedrange (e.g., weight percentages or carbon groups) includes each specificvalue, integer, decimal, or identity within the range. Any listed rangecan be easily recognized as sufficiently describing and enabling thesame range being broken down into at least equal halves, thirds,quarters, fifths, or tenths. As a non-limiting example, each rangediscussed herein can be readily broken down into a lower third, middlethird and upper third, etc. As will also be understood by one skilled inthe art, all language such as “up to”, “at least”, “greater than”, “lessthan”, “more than”, “or more”, and the like, include the number recitedand such terms refer to ranges that can be subsequently broken down intosub-ranges as discussed above. In the same manner, all ratios recitedherein also include all sub-ratios falling within the broader ratio.Accordingly, specific values recited for radicals, substituents, andranges, are for illustration only; they do not exclude other definedvalues or other values within defined ranges for radicals andsubstituents. It will be further understood that the endpoints of eachof the ranges are significant both in relation to the other endpoint,and independently of the other endpoint.

One skilled in the art will also readily recognize that where membersare grouped together in a common manner, such as in a Markush group, theinvention encompasses not only the entire group listed as a whole, buteach member of the group individually and all possible subgroups of themain group. Additionally, for all purposes, the invention encompassesnot only the main group, but also the main group absent one or more ofthe group members. The invention therefore envisages the explicitexclusion of any one or more of members of a recited group. Accordingly,provisos may apply to any of the disclosed categories or embodimentswhereby any one or more of the recited elements, species, orembodiments, may be excluded from such categories or embodiments, forexample, for use in an explicit negative limitation.

The term “contacting” refers to the act of touching, making contact, orof bringing to immediate or close proximity, including at the cellularor molecular level, for example, to bring about a chemical reaction, ora physical change, e.g., in a solution, in a reaction mixture.

An “effective amount” refers to an amount effective to bring about arecited effect, such as an amount necessary to form products in areaction mixture. Determination of an effective amount is typicallywithin the capacity of persons skilled in the art, especially in lightof the detailed disclosure provided herein. The term “effective amount”is intended to include an amount of a compound or reagent describedherein, or an amount of a combination of compounds or reagents describedherein, e.g., that is effective to form products in a reaction mixture.Thus, an “effective amount” generally means an amount that provides thedesired effect.

The term “substantially” as used herein, is a broad term and is used inits ordinary sense, including, without limitation, being largely but notnecessarily wholly that which is specified. For example, the term couldrefer to a numerical value that may not be 100% the full numericalvalue. The full numerical value may be less by about1%, about 2%, about3%, about 4%, about 5%, about 6%, about 7%, about 8%, about 9%, about10%, about 15%, or about 20%.

As used herein, the term “substituted” or “substituent” is intended toindicate that one or more (for example., 1-20 in various embodiments,1-10 in other embodiments, 1, 2, 3, 4, or 5; in some embodiments 1, 2,or 3; and in other embodiments 1 or 2) hydrogens on the group indicatedin the expression using “substituted” (or “substituent”) is replacedwith a selection of group(s), or with a suitable group known to those ofskill in the art, provided that the indicated atom's normal valency isnot exceeded, and that the substitution results in a stable compound.Similarly, the carbon(s) (or carbon atom(s)) indicated in a Formuladisclosed herein can have a suitable substituent or group known to thoseof skill in the art.

Suitable substitutions or substituents include, for example, alkyl,alkenyl, alkynyl, alkoxy, halo, haloalkyl, hydroxy, hydroxyalkyl, aryl,heteroaryl, heterocycle, cycloalkyl, alkanoyl, alkoxycarbonyl, amino,alkylamino, dialkylamino, trifluoromethylthio, difluoromethyl,acylamino, nitro, trifluoromethyl, trifluoromethoxy, carboxy,carboxyalkyl, keto, thioxo, alkylthio, alkylsulfinyl, alkylsulfonyl, andcyano. Additionally, non-limiting examples of substituents that can bebonded to a substituted carbon (or other) atom include F, Cl, Br, I,OR′, OC(O)N(R′)₂, CN, CF₃, OCF₃, R′, O, S, C(O), S(O), methylenedioxy,ethylenedioxy, N(R′)₂, SR′, SOR′, SO₂R′, SO₂N(R′)₂, SO₃R′, C(O)R′,C(O)C(O)R′, C(O)CH₂C(O)R′, C(S)R′, C(O)OR′, OC(O)R′, C(O)N(R′)₂,OC(O)N(R′)₂, C(S)N(R′)₂, (CH₂)₀₋₂NHC(O)R′, N(R′)N(R′)C(O)R′,N(R′)N(R′)C(O)OR′, N(R′)N(R′)CON(R′)₂, N(R′)SO₂R′, N(R′)SO₂N(R′)₂,N(R′)C(O)OR′, N(R′)C(O)R′, N(R′)C(S)R′, N(R′)C(O)N(R′)₂,N(R′)C(S)N(R′)₂, N(COR')COR′, N(OR′)R′, C(═NH)N(R′)₂, C(O)N(OR′)R′, orC(═NOR′)R′ wherein R′ can be hydrogen or a carbon-based moiety, andwherein the carbon-based moiety can itself be further substituted. Whena substituent is monovalent, such as, for example, For Cl, it is bondedto the atom it is substituting by a single bond. When a substituent ismore than monovalent, such as O, which is divalent, it can be bonded tothe atom it is substituting by more than one bond, i.e., a divalentsubstituent is bonded by a double bond; for example, a C substitutedwith O forms a carbonyl group, C═O, wherein the C and the O are doublebonded. Alternatively, a divalent substituent such as O, S, C(O), S(O),or S(O)₂ can be connected by two single bonds to two different carbonatoms. For example, O, a divalent substituent, can be bonded to each oftwo adjacent carbon atoms to provide an epoxide group, or the O can forma bridging ether group between adjacent or non-adjacent carbon atoms,for example bridging the 1,4-carbons of a cyclohexyl group to form a[2.2.1]-oxabicyclo system. Further, any substituent can be bonded to acarbon or other atom by a linker, such as (CH₂)_(n) or (CR′₂)_(n)wherein n is 1, 2, 3, or more, and each R′ is independently selected.

The term “halo” or “halide” refers to fluoro, chloro, bromo, or iodo.Similarly, the term “halogen” refers to fluorine, chlorine, bromine, andiodine.

The term “alkyl” refers to a branched or unbranched hydrocarbon having,for example, from 1-20 carbon atoms, and often 1-12, 1-10, 1-8, 1-6, or1-4 carbon atoms. As used herein, the term “alkyl” also encompasses a“cycloalkyl”, defined below. The alkyl can be unsubstituted orsubstituted, for example, with a substituent described above. The alkylcan also be optionally partially or fully unsaturated.

The term “cycloalkyl” refers to cyclic alkyl groups of, for example,from 3 to 10 carbon atoms having a single cyclic ring or multiplecondensed rings. The cycloalkyl can be unsubstituted or substituted. Thecycloalkyl group can be monovalent or divalent, and can be optionallysubstituted as described for alkyl groups. The cycloalkyl group canoptionally include one or more cites of unsaturation, for example, thecycloalkyl group can include one or more carbon-carbon double bonds.

The term “enantiomerically enriched” (“ee”) as used herein refers tomixtures that have one enantiomer present to a greater extent thananother. Reactions that provide one enantiomer present to a greaterextent than another would therefore be “enantioselective” (ordemonstrate “enantioselectivity”). In one embodiment of the invention,the term “enantiomerically enriched” refers to a mixture having at leastabout 2% ee to about 99% ee. The term “enantiomerically enriched”includes enantiomerically pure mixtures which are mixtures that aresubstantially free of the species of the opposite optical activity orone enantiomer is present in very low quantities, for example, 0.01%,0.001% or 0.0001%.

The term, “repeat unit”, “repeating unit”, or “block” as used hereinrefers to the moiety of a polymer that is repetitive. The repeat unitmay comprise one or more repeat units, labeled as, for example, repeatunit A, repeat unit B, repeat unit C, etc. Repeat units A-C, forexample, may be covalently bound together to form a combined repeatunit. Monomers or a combination of one or more different monomers can becombined to form a (combined) repeat unit of a polymer or copolymer.

The term “molecular weight” for the copolymers disclosed herein refersto the average number molecular weight (M_(n)). The corresponding weightaverage molecular weight (Mw) can be determined from other disclosedparameters by methods (e.g., by calculation) known to the skilledartisan.

The copolymers disclosed herein can comprise random or block copolymers.The copolymers described herein as random copolymers, are indicated bythe “r” over the bond between the units of the copolymer. The copolymersdescribed herein as block copolymers, are indicated by the “b” over thebond between the units of the copolymer.

In various embodiments, unless otherwise stated, the ends of thecopolymer (i.e., the initiator end or terminal end), is a low molecularweight moiety (e.g. under 500 Da), such as, H, OH, OOH, CH₂OH, CN, NH₂,or a hydrocarbon such as an alkyl (for example, a butyl or2-cyanoprop-2-yl moiety at the initiator and terminal end), alkene oralkyne, or a moiety as a result of an elimination reaction at the firstand/or last repeat unit in the copolymer. In this disclosure the end ofthe polymer can also be Ph₂CHCH₂O—.

Embodiments of the Invention

This disclosure provides a polymer comprising Formula I, Formula II, orFormula III:

wherein

Q and R are the terminal ends of the polymer, or Q and R taken togetherform a cyclic polymer of Formula I, Formula II, or Formula III;

G is O, S, or NR^(z);

R^(x), R^(y) and R^(z) are each independently H or —(C₁-C₈)alkyl;

m is about 20 to about 10¹⁰; and

n is 1-20;

wherein the R^(y) substituents have a trans-configuration relative toeach other, each —(C₁-C₈)alkyl moiety is independently branched orunbranched, and each ring-embedded carbon (other than the carbonssubstituted with R^(y)) independently has an optional —(C₁-C₈)alkylsubstituent or phenyl substituent.

In various other embodiments, each or the carbon atoms in the ringportion of Formulas I-III is independently substituted with an alkylgroup or an aryl group, wherein the alkyl group is branched orunbranched, the alkyl group is optionally substituted, and the arylgroup (e.g., a phenyl) is optionally substituted.

In some embodiments of the polymer of Formulas I-III, G is O. In otherembodiments, R^(x) is H, or R^(y) is H. In yet other embodiments, m isabout 2 to about 20 or to about 10²⁰. In some other embodiments, n is 0to about 50. In further embodiments, Q is —(C₁-C₈)alkyl, N(R^(A))₂,OR^(A), or SR^(A), and R is H, wherein each R^(A) is independently H,—(C₁-C₈)alkyl, Ph₂CHCH₂—, or —Si[(C₁-C₈)alkyl]₃.

In yet other embodiments, one or more ring-embedded carbons furthercomprise a (C₁-C₈)alkyl substituent or aryl substituent, and/oroptionally the carbon atom of the —CH₂— moiety of the —C(R^(y))CH₂G—group of Formula I or the —C(R^(y))CH₂C(═O)— group of Formula II furthercomprises a —(C₁-C₈)alkyl substituent, or aryl substituent. Inadditional embodiments, the IV substituents of Formula III have acis-configuration or a trans-configuration relative to each other. Insome other embodiments, the —(C₁-C₈)alkyl substituent is furthersubstituted.

In additional embodiments, the polymer has a number average molecularweight (M_(n)) of about 0.1 kg mol⁻¹ to about 5×10⁶ kg mol⁻¹, and/or thepolymer has a polydispersity index of about 1 to about 3. In furtherembodiments, Mn can be about 10⁵ kg mol⁻¹, about 10⁴ kg mol⁻¹, about 10³kg mol⁻¹, about 10² kg mol⁻¹, about 10 kg mol⁻¹, or about 1 kg mol⁻¹. Inother embodiments, the stereochemistry of the repeating unit (m) is (R,R) or (S, S). The stereochemistry can also be (R, S), (S, R), (R, R),(S, S), or a combination thereof.

In further embodiments, the polymer is thermally depolymerizable orchemically depolymerizable to a monomer. In yet other embodiments,thermal or chemical depolymerization of the polymer provides about 95%or greater conversion of the polymer to the monomer (wherein the monomeris the monomer that can form the polymer by the ring openingpolymerization reaction described herein). In other embodiments, thepolymer provides about 50% to about 95% conversion of the polymer to themonomer.

This disclosure also provides a method for polymerization comprisingcontacting a monomer with a catalyst and an optional protic initiator toform a polymer via ring opening polymerization reaction of the monomer,wherein the monomer is a monomer of Formula I or Formula V:

or an enantiomer or mixture thereof, wherein

G¹ is —C(═O)— and G² is O, S, or NR^(z); or

G¹ is O, S, or NR^(z) and G² is —C(═O)—;

G³ is O, S, or NR^(z);

R^(x), R^(y) and R^(z) are independently H or (C₁-C₈)alkyl; and

n is 0-20;

wherein each —(C₁-C₈)alkyl moiety is independently branched orunbranched, and each ring-embedded carbon independently has an optional—(C₁-C₈)alkyl substituent or phenyl substituent.

In various other embodiments, the polymer is formed at a pressure ofabout 1 atm to about 10 atm and at a temperature of about 0° C. to about100° C. In other embodiments, the pressure is about 1 atmosphere toabout 100 atmospheres. In yet other embodiments, the temperature isabout −20° C. to about 200° C.

In additional embodiments, the catalyst is a metal-based catalyst or anorganic catalyst. In other embodiments, the organometallic catalystcomprises a nucleophile and a lanthanide metal or a transition metal. Inyet other embodiments, the organometallic catalyst istris[N,N-bis(trimethylsilyl)amide]lanthanum(III),

wherein X is a donor solvent molecule.

In further embodiments, the protic initiator is an alcohol, a thiol, oran amine. In other embodiments, the protic initiator is, for example,Ph₂CHCH₂OH, hexanol, dipropylamine, or a combination thereof.

In yet other embodiments, the described methods may further comprise asolvent, wherein the solvent is any effective solvent. For example, thesolvent can be a non-protic or protic solvent. The solvent can be, forexample, but not limited to, dichloromethane (DCM), toluene,tetrahydrofuran, ether, xylene, or a combination of solvents. In someembodiments, the disclosed method may not require a solvent (e.g., thereaction is performed “neat”).

In additional other embodiments, the monomer (M), catalyst (C), andinitiator (I) are contacted at various ratios of M:C:I. In someembodiments, the value of M in the ratio M:C:I can range from about 1 toabout 100,000, about 10 to about 10,000, or about 100 to about 1000. Inother embodiments, the value of C in the ratio M:C:I can range fromabout 0.1 to about 1,000, about 0.5 to about 500, or about 1 to about100. In yet other embodiments, the value of I in the ratio M:C:I canrange from about 0 to about 1,000, about 0 to about 100, or about 0 toabout 10.

In yet other additional embodiments, the monomer is a monomer of FormulaIVA or Formula IVB:

or an enantiomer or mixture thereof, wherein n is 1-20. In some variousembodiments, n is 1-6, n is 1-4, or n is 0-50. In some otherembodiments, the monomer is a monomer of Formula IVC or Formula IVD:

or an enantiomer or mixture thereof, wherein n is 1-20.

Various embodiments of the disclosed methods further comprise quenchingthe polymerization reaction to form a polymer. In other embodiments, aprotic source is used for quenching, such as, but not limited to,chloroform, an acid (e.g., HCl), or water.

In some embodiments of the invention, the monomer is a monomer ofFormula IVA:

-   or an enantiomer or mixture thereof, wherein n is 1-20;-   the catalyst comprises a nucleophile (Q); and-   the polyester is a polyester of Formula VI (or Formula VIB):

the enantiomer, racemate or mixture of diastereoisomers thereof;

wherein

-   -   Q is the nucleophile and R is H, or Q and R taken together form        a cyclic polymer of Formula VI (or Formula VIB); and    -   m is about 20 to about 10¹⁰.

In some other embodiments of the invention, the monomer is a monomer ofFormula IVB:

-   or an enantiomer or mixture thereof, wherein n is 1-20;-   the catalyst comprises a nucleophile (Q); and-   the polyester is a polyester of Formula VII (or Formula VIIB):

the enantiomer, racemate or mixture of diastereoisomers thereof;

wherein

-   -   Q is the nucleophile and R is H, or Q and R taken together form        a cyclic polymer of Formula VII (or Formula VIIB); and m is        about 20 to about 10¹⁰.

In various other embodiments, m is about 5 to about 10⁸, or about 10⁷,about 10⁶, about 10⁵, about 10⁴ or about 10³. In some other embodiments,the polymer (for example a polyester) has a polydispersity index ofabout 1 to about 2, about 1 to about 1.5, or about 0.5 to about 2.5.

In various other embodiments of the disclosed methods further comprisescontacting the polymerization reaction with a second monomer. In someembodiments, the second monomer is a lactone or lactide. In additionalembodiments, a block or random copolymer is formed by contacting thepolymerization reaction with a second monomer.

In other additional embodiments, the polymer is recycled to the monomerby thermal depolymerization or chemical depolymerization. In furtherembodiments, stoichiometric amounts of a polymer (e.g., a polyester)having a stereo-configuration formed from one enantiomer of the monomer,and a second polymer (e.g., a second polyester) having the oppositestereo-configuration formed from the other enantiomer of the monomer areco-crystallized to form a crystalline stereocomplex, wherein thecrystalline stereocomplex has a higher melting temperature than saidpolymer (or polyester) having the stereo-configuration or oppositestereo-configuration.

In various embodiments, the disclosed polyester is prepared according tothe methods described herein, wherein the polyester is a polyester ofFormula VI. In other various embodiments, the disclosed polyester isprepared according to the method described herein, wherein the polyesteris a polyester of Formula VII.

This disclosure provides ranges, limits, and deviations to variablessuch as volume, mass, percentages, ratios, etc. It is understood by anordinary person skilled in the art that a range, such as “numberl” to“number2”, implies a continuous range of numbers that includes the wholenumbers and fractional numbers. For example, 1 to 10 means 1, 2, 3, 4,5, . . . 9, 10. It also means 1.0, 1.1, 1.2. 1.3, . . . , 9.8, 9.9,10.0, and also means 1.01, 1.02, 1.03, and so on. If the variabledisclosed is a number less than “number 10”, it implies a continuousrange that includes whole numbers and fractional numbers less thannumber 10, as discussed above. Similarly, if the variable disclosed is anumber greater than “number 10”, it implies a continuous range thatincludes whole numbers and fractional numbers greater than number 10.These ranges can be modified by the term “about”, whose meaning has beendescribed above.

Results and Discussion Room Temperature, Solvent-Free Polymerization toHigh-Molecular Weight Polymers

To design monomer and polymer structures that can deliver desiredproperties, it is advantageous to keep the highly stable, five-memberedGBL core so that the complete chemical recyclability of the designedpolymers can be preserved (for both thermodynamic and kinetic reasons).We reasoned that the ring strain of the parent (nonstrainedfive-membered GBL), or the thermodynamic polymerizability, can be tunedvia suitable substituents and substitution patterns on the GBL ring.trans-Hexahydro-2(3H)-benzofuranone [i.e., 4,5-trans six-memberedring-fused GBL (4,5-T6GBL)] was found to be polymerizable even at 40° C.by typical anionic initiators but not by a coordination polymerizationcatalyst such as tin(II) octoate, whereas the cis-fused isomer iscompletely inert toward ROP. However, the resulting product was reportedto be only an oligomer, with a number-average molecular weight (M_(n))up to only 6.2 kg/mol [by gel permeation chromatography (GPC)] or 2.6kg/mol [by nuclear magnetic resonance (NMR)].

We hypothesized that removing the substituent at the 5 (or γ) positionof the GBL ring could not only further enhance the thermodynamicpolymerizability (by increasing the ring strain) and rate ofpolymerization (by releasing the steric pressure at the ester —OC_(α)H),thus affording useful high-molecular weight polymers in short timeperiods, but also render polymers with possibly high crystallinityassisted by ordered secondary structures and/or OC_(α)H—O═C hydrogenbonds between polyester chains. Guided by these hypotheses, we arrivedat 3,4-T6GBL (M1), where the cyclohexyl ring is trans-fused to GBL atthe α and β positions and the γ position is left unsubstituted toenhance polymerizability, reaction rates, and H bonding. This monomercan be prepared on relatively large scales from commercially availabletrans-1,2-cyclohexanecarboxylic acid anhydride.

The polymerizability of M1 was probed via measuring the thermodynamicsof its ROP with a discrete molecular catalyst, yttrium complex Y1 (FIG.1A), which is known to be effective for the ROP of the parent GBL,revealing standard-state thermodynamic parameters of ΔH°_(p)(change inenthalpy of polymerization)=−20 kJ mol⁻¹ and ΔS°_(p) (change in entropyof polymerization)=−72 mol⁻¹K⁻¹. The T_(c) was calculated to be 0°, 62°,or 88° C. for an initial M1 concentration ([M1]₀) of 1.0, 5.0, and 8.2(bulk) M, respectively. These data showed that M1 exhibits much higherthermodynamic polymerizability than GBL, as indicated by a much largernegative change in enthalpy and a substantially elevated T_(c):ΔH°_(p)=−20 kJ mol⁻¹ versus −5.4 kJ mol⁻¹ and T_(c)=0° C. (1.0 M) versus−136° C. (1.0 M) for the ROP of M1 and GBL, respectively. Accordingly,we chose the solvent-free, bulk condition to perform the polymerizationat room temperature, as summarized in Table 1.

Quantitative conversion of M1 was achieved even with common anionicinitiators such as potassium tert-butoxide and TBD(1,5,7-triazabicyclo[4.4.0]dec-5-ene), but the product was not that of apolymer; instead, M1 was isomerized under the basic conditions to itscis isomer, which is nonpolymerizable, as verified by its independentsynthesis and subsequent polymerization surveys with different catalystsand conditions (Table 2). To overcome this isomerization issue, we useda coordinative-insertion ROP catalyst, La[N(SiMe₃)₂]₃(where Me ismethyl) (La1), as La is more earth abundant and less expensive withinthe lanthanide series and was demonstrated to be effective for the ROPof GBL.

La1 exhibited high selectivity and activity toward the ROP to affordpoly-M1[P(M1)], achieving greater than 80% conversion with 0.2 or 0.1mole % (mol %) catalyst loading. For example, with a monomer(M)/catalyst (cat)/initiator (I) ratio of [M1]/[La1]/[Ph₂CHCH₂OH] (wherePh is phenyl)=500/1/3, the ROP occurred rapidly to reach 73% M1conversion in under 1 min. At 82% conversion, the isolated P(M1) wasmeasured by a GPC instrument equipped with multi (18)—angle lightscattering and differential refractive index detectors to have a mediumM_(n) of 21.0 kg/mol and an extremely low dispersity index (Ð) value of1.01; this measured M_(n) is close to the calculated M_(n) of 19.4kg/mol, thus indicating a high initiation efficiency of 92%. Loweringthe catalyst loading to 0.1 mol % (1000/1/3 ratio) still achieved arelatively high conversion of 84%, producing P(M1) with M_(n)=46.0kg/mol and Ð=1.01.

To further increase the molecular weight of the resulting P(M1), theM/cat/I ratio was increased to 5000/1/3 with a catalyst loading of 0.02mol %, affording P(M1) a further enhanced M_(n) (67.9 kg/mol) and astill low Ð (1.01) at 45% conversion. The absolute molecular weightmeasured by GPC (M_(n)=21.0 kg/mol, Ð=1.01) (Table 1, run 2) was closeto both the M_(n) of 19.4 kg/mol calculated on the basis of the [M1]/[I]ratio (Table 1) and the M_(n) of 19.9 kg/mol calculated on the basis ofthe chain ends of the polymer characterized by NMR, the latter of whichalso revealed a linear structure {linear P(M1) [l-P(M1)]} and showedhigh end-group fidelity.

The linear structure of the P(M1) produced by La1 with ROH (where R isPh₂CHCH₂O) was further confirmed by matrix-assisted laserdesorption/ionization—time-of-flight mass spectroscopy (MALDI-TOF MS) ofa low-molecular weight sample. Specifically, the MS spectrum (FIG. 7)consisted of only one series of molecular ion peaks, with the spacingbetween the two neighboring molecular ion peaks corresponding to theexact molar mass of the repeat unit, M1 [mass/charge ratio(m/z)=140.18], as shown by the slope (140.14) of the linear plot of m/zvalues (y axis) versus the number of M1 repeat units (x axis). Theintercept of the plot, 221.8, represents the total mass of chain endsplus the mass of Na⁺ [M_(cnd)=198.3 (Ph₂CHCH₂O/H) g/mol+23.0 (Na⁺)g/mol], corresponding to linear structure Ph₂CHCH₂O—[M1]_(n)—H.

With the demonstrated ability of La1 to form PGBL with a cyclicstructure when no initiating ROH is added, we explored the possibilityof producing cyclic polymer c-P(M1) by using La1 alone. Thepolymerizations with different catalyst loadings (1.0 to 0.05 mol % La1)were rapid and achieved relatively high monomer conversions, from 79 to84%. Unlike the controlled polymerization with La1 and 3ROH, where the[M1]/[La1] ratio could determine the M_(n) while maintaining a low Ðvalue of 1.01 for all the l-P(M1) materials produced (Table 1), thepolymerizations with La1 alone afforded polymers with similar M_(n)values in a narrow range of 73.0 to 85.5 kg/mol coupled with higher Ðvalues from 1.34 to 1.48, despite a 20-fold change in the [M1]/[La1]ratio and a 7-fold change in the reaction scale (Table 1).

These observations indicated that possible cyclization reactionsoccurred under the neat and room temperature conditions used once acertain chain length was reached, which would create a cyclic polymerstructure, c-P(M1). Consistent with this proposed scenario, no endgroups were detected from the NMR spectra of the polymers produced byusing La1 alone. Analysis of a low-molecular weight sample by MALDI-TOFMS (FIG. 6) also revealed no end groups (the linear plot of m/z valuesversus the number of M1 repeat units gave an intercept of 23,corresponding to the mass of Na⁺). The cyclic structure of c-P(M1) wasfurther confirmed by GPC analysis with triple detection by alight-scattering detector, a refractometer, and a viscometer.

A double-logarithm (Mark-Houwink-Sakurada) plot of intrinsic viscosity[η] versus absolute weight-average molecular weight (M_(w)) in the lowermolecular weight regime (FIG. 1B) showed a lower intrinsic viscosity forc-P(M1), due to a smaller hydrodynamic volume, than for l-P(M1). The[η]_(cyclic)/[η]_(linear) ratio was found to be 0.7, which is inagreement with the theoretically predicted value for this ratio and theexperimentally observed value for other cyclic polymers. Expanding to anoptically active cyclic polymer structure, we synthesized two chiralpolymers with similar M_(w) values from the ROP of (R)-M1 with La1 andROH and with La1 alone. The logarithm plots of M_(w) versus the elutionvolume revealed that the chiral polymer P[(R)-M1] obtained in theabsence of ROH was eluted later than the polymer obtained in thepresence of ROH (FIG. 1C). By analogy to achiral P(M1), it can belikewise assigned to a cyclic structure because its hydrodynamic volumeis smaller than that of its linear analog.

The synthesis of pure cyclic polymers with appreciable (medium to high)molecular weights, which are critical for polymer topology-propertyrelationship studies, still presents a challenge for many types ofpolymers. This problem has led to substantial interest in developingsynthetic methodologies for cyclic polymers, such as the ring-openingmetathesis polymerization route to cyclic polyethylene and theN-heterocyclic carbene-mediated zwitterionic polymerization route tocyclic polylactide and poly(α-peptoid)s. The cleaner formation ofc-P(M1) than of cyclic PGBL, as demonstrated by the NMR, MS spectra, and[η]_(cyclic)/[η]_(linear)ratio, is noteworthy.

As the molecular weight of the cyclic polymer is limited by thepropensity to cyclize once a certain chain length is reached during thepolymerization, we explored other catalyst-initiator systems that couldfurther increase the molecular weight of l-P(M1). In this context, wearrived at discrete yttrium complex Y1 supported by the tetradentateamino-bisphenolate ligand bearing a pendant ether group, which has beenshown to be highly efficient in the ROP of lactide and lactones. With Y1as the catalyst and catalyst loading as low as 50 parts per million(ppm), we achieved relatively high M1 conversions of 80 to 91% (Table1). Thus, in a 10-g polymerization, a high-molecular weight P(M1) withM_(n)=1.11×10⁶ g/mol (Ð=1.09) was readily produced under neat and roomtemperature conditions with only 50 ppm Y1. Furthermore, the molecularweight of the resulting polymer could be readily controlled by theaddition of the ROH (Ph₂CHCH₂OH) initiator; thus, with the [M1]/[Y1]ratio of 10000/1 held constant, the equivalent of ROH added (relative toY1) was varied from 25 to 50 to 100, affording l-P(M1) withcorrespondingly reduced M_(n) values from 49.2 kg/mol (Ð=1.01) to 18.4kg/mol (Ð=1.01) to 11.6 kg/mol (Ð=1.01) (Table 1).

These M_(n) values were close to the M_(n) values calculated on thebasis of the [M1]/[ROH] ratio and Miconversion data, thus demonstratinga high initiation efficiency of >96%. Overall, Y1 brings about“immortal” ROP of M1 in the presence of ROH, producing well-definedl-P(M1) materials with near ideal dispersity (1.01) in a catalyticfashion (affording up to 100 polymer chains per Y1).

An environmentally more benign and earth-abundant zinc catalyst,2,6-diisopropylphenylsubstituted β-diiminate zinc isopropoxide complex[(BDI)ZnO^(i)Pr] (Zn1), was also examined for the ROP of M1 at roomtemperature under neat conditions. The results, summarized in Table 1,showed that Zn1 is also highly effective for this polymerization. Forexample, with catalyst loading of 0.02 mol %, the ROP achieved 82%conversion in 3 hours, producing P(M1) with a high M_(n) of 307 kg/moland an extremely narrow Ð of 1.01. Comparing these data with thoseobtained with Y1—12 hours, 87% conversion, M_(n)=363 kg/mol, andÐ=1.15—under the same conditions shows that, under this set ofconditions (room temperature, neat conditions, 0.02 mol % catalyst), theZn catalyst performed better than the Y catalyst in terms of its higherpolymerization activity and lower polymer dispersity.

TABLE 1 Results of ROP of M1 Time^(b) Conv. M_(n) ^(c) M_(n,calcd)d

^( c) Run^(a) Cat. [M]/[Cat.]/[I] Solvent (h) (%)^(b) (kg/mol) (kg/mol)(M_(w)/M_(n))  1 La1  500/1/3 neat 1 (min) 73 n.d. 17.2 n.d.  2 La1 500/1/3 neat 1 82 21.0 19.4 1.01  3 La1  1000/1/3 neat 1 84 46.0 39.41.01  4^(e) La1  5000/1/3 neat 7 45 67.9 105 1.01  5 La1  100/1/0 neat 384 82.0 — 1.43  6 La1  200/1/0 neat 3 80 85.5 — 1.48  7 La1  500/1/0neat 3 79 76.0 — 1.48  8 La1  1000/1/0 neat 3 84 73.0 — 1.34  9 La1 2000/1/0 neat 3 80 81.4 — 1.41 10^(f) La1  2000/1/0 neat 6 85 81.0 —1.35 11 La1  200/1/0 tol (6.5M) 1 70 15.5 — 1.49 12^(g) La1  200/1/0 tol(4.0M) 1 26 21.5 — 1.39 13^(h) La1  200/1/0 neat 1 71 15.8 — 1.26 14 Y1 500/1 neat 3 88 93.7 — 1.34 15^(e) Y1  2000/1 neat 12 86 226 — 1.2316^(e) Y1  5000/1 neat 12 87 363 — 1.15 17^(e) Y1 20000/1 neat 12 80 399— 1.17 18^(f) Y1 20000/1 neat 12 91 729 — 1.12 19^(i) Y1 20000/1 neat 1288 875 — 1.07 20^(j) Y1 20000/1 neat 12 85 1110 — 1.09 21^(e) Y110000/1/25 neat 24 84 49.2 47.3 1.01 22^(e) Y1 10000/1/50 neat 24 8118.4 22.9 1.01 23^(e) Y1 10000/1/100 neat 24 80 11.6 11.4 1.01 24 Zn1 200/1 neat 1 87 27.1 — 1.02 25 Zn1  1000/1 neat 3 80 156 — 1.01 26^(e)Zn1  5000/1 neat 3 82 307 — 1.01 27^(e) Zn1 20000/1 neat 12 62 588 —1.02 ^(a)General conditions (unless marked otherwise): M1 = 421 mg,initiator (I) = Ph₂CHCH₂OH, room temperature (~25° C.), n.d. = notdetermined. ^(b)Polymerizations typically occurred rapidly in mins andceased stirring, and then the reaction was left without stirring for theindicated time period. Monomer conversion was determined by ¹H NMR inCDCl₃. ^(c)Number-average molecular weight (M_(n)) and dispersity index( 

 = M_(w)/M_(n)) determined by gel-permeation chromatography (GPC) at 40°C. in CHCl₃ coupled with a DAWN HELEOS II multi (18)-angle lightscattering detector and an Optilab TrEX dRI detector for absolutemolecular weights. ^(d)Calculated based on: ([M]₀/[I]₀) × Conv. % ×(molecular weight of M1) + (molecular weight of I). ^(e)Catalystdissolved in 10 μL of toluene (tol). ^(f)M1 = 2.8 g. ^(g)Performed at 0°C. ^(h)Performed at 40° C. ^(i)M1 = 11.0 g. ^(j)M1 = 10.0 g, with moreefficient stirring.

Thermostability, Chemical Recyclability, and Circular M1-P(M1)-M1 Cycle

The thermostability of both linear and cyclic P(M1) materials wasexamined by thermogravimetric analysis (TGA) in terms of onsetdecomposition temperature T_(d) (defined by the temperature of 5% weightloss) and maximum decomposition temperature T_(max) [defined by the peakvalue in the relative derivative thermogravimetry (DTG)]. Comparing TGAcurves of the cyclic and linear polymers revealed that c-P(M1) producedwith La1 alone had a noticeably higher T_(d) (337° C.) than l-P(M1)obtained with [M1]/[La1]/[Ph₂CHCH₂OH]=500/1/3, with T_(d)=316° C. (FIG.2A), although the T_(max) values were similar (390° versus 394° C.). TheT_(d) and T_(max) of l-P(M1) were 115° and 176° C. higher, respectively,than those of the linear PGBL (obtained with[GBL]/[La1]/[Ph₂CHCH₂OH]=400/1/3), which had a T_(d) of 201° C. and aT_(max) of 218° C. The l-P(M1) produced by Y1 ([M1]/[Y1]=2000) was evenmore thermally robust, with a high T_(d) of 342° C. and a T_(max) of391° C. (FIG. 2B). The T_(d) (344° C.) of the physical blend of 1:1P[(R)-M1]−P[(S)-M1] was found to be about 17 to 21° C. higher than thoseof the respective enantiomeric polymers (FIG. 17), whereas the Tmaxvalues varied only slightly (FIG. 2B).

The chemical recyclability of P(M1) materials was examined by boththermolysis at high temperatures and chemolysis in the presence of acatalyst at milder temperatures. An 1-P(M1) sample (M_(n)=46.0 kg/mol,267=1.01) prepared with [M1]/[La1]/[Ph₂CHCH₂OH]=1000/1/3 was heated in asealed tube at ≥300° C. for 1 hour; gravimetric and NMR analyses of theresulting colorless liquid showed that monomer M1 was recovered in apure state at a quantitative yield. Likewise, heating a c-P(M1) sample(M_(n)=82.0 kg/mol, Ð=1.43) prepared with [M1]/[La1]=100/1 at ≥300° C.for 24 hours also afforded the recycled monomer in a pure state at aquantitative yield. To reduce the energy input in the recycling process,the chemical recyclability of P(M1) was also investigated by chemolysiswith a catalytic amount of a simple metal salt (ZnCl₂) at 120° C. Thus,subjecting either l-P(M1) or c-P(M1) (FIG. 2C) to the above-listed mildchemolysis conditions also demonstrated the full chemical recyclability.

The circular monomer-polymer-monomer cycle was examined through threeconsecutive polymerization-depolymerization cycles on a multigram scale.Thus, pure M1 was first polymerized by Zn1 to well-defined P(M1)(Ð=1.01) after achieving 85% conversion, which is the typical conversionachieved under the ambient temperature and neat conditions used (theunreacted monomer can be recovered). The isolated and purified P(M1) wasthen subjected to chemolysis in the presence of a simple metal salt(ZnCl₂, 2 mol %) at 180° C. under vacuum pressure (0.01 torr); thecollected colorless liquid was confirmed to be pure M1 by ¹H NMRanalysis. The recovered monomer (97% isolated yield) was repolymerizeddirectly without further purification by Zn1 to produce well-definedP(M1) (Ð=1.02), achieving the same conversion (85%). This process wasrepeated three times, and the mass balance of the regenerated polymerproduct and the recovered monomer was tracked over the three consecutivepolymerization-depolymerization cycles, showing essentially quantitativerecovery of pure M1 (96 to 97% isolated yield) after each cycle. Thisrecovered M1 can be directly repolymerized without a decrease in thesubsequent monomer conversion and polymer quality.

Physical Blending to Yield Highly Crystalline Stereocomplexed Material

Physical blending of enantiomers of certain chiral polyesters in astoichiometric ratio offers a powerful strategy to generate crystallinestereocomplexed (sc) materials that often exhibit much enhancedmaterials properties, such as increased T_(m) and crystallization rate,compared with their constituent enantiomers. In this context, a 1:1physical blend of enantiomeric isotactic polymers (Table 2) derived fromenantiomeric monomers, either linear enantiomers l-P[(R)-M1] andl-P[(S)-M1] produced with [M1]/[Y1]=1000/1 or cyclic enantiomersc-P[(R)-M1] and c-P[(S)-M1] produced with [M1]/[La1]=500/1, showedsubstantially different thermal properties and solubility as well asnoticeably different spectroscopic features from the parent enantiomers.Differential scanning calorimetry (DSC) curves for the first heatingscans (FIG. 3A) of the linear enantiomeric polymers, previouslycrystallized from CHCl₃, displayed a crystalline peak with T_(m)=126° C.(heat of fusion ΔH_(m)=28 to 32 J/g), but the 1:1 blend produced muchhigher melting and heat of fusion values, with T_(m)=203° C. andΔH_(m)=53 J/g. More notably, on the second heating scans (after coolingat 10° C./min) only the physical blend continued to show a melting peakof T_(m)=188° C. (T_(c)=108° C.), whereas the enantiomeric polymersbecame amorphous, displaying only a glass transition temperature T_(g)of ˜49° C. (FIG. 3B). These results indicate that these enantiomericpolymers have relatively low crystallization rates and thatstereocomplexation in the blend markedly enhanced not only thecrystallinity but also the crystallization rate. Linear enantiomericpolymers produced by the [La1]-3[Ph₂CHCH₂OH] system displayed more orless the same DSC curves on the first and second heating scans (FIG. 18and FIG. 19). Furthermore, a comparison of DSC curves for c-P(M1) showedthe same trend: The first heating scans revealed a T_(m) of 127° C.(ΔH_(m)=34 to 37 J/g) for the enantiopure polymers but a much higherT_(m) of 198° C. and ΔH_(m) of 61 J/g for the c-P[(R)-M1]−c-P[(S)-M1]blend (FIG. 20 and FIG. 21), and the second heating scans showed amelting peak of T_(m)=188° C. (T_(c)=122° C.) only for the blend (FIG.21).

Overlays of Fourier transform infrared (FTIR) spectra in the carbonylstretching region (FIG. 3C and FIG. 21) revealed the red shift of theC═O stretching frequency (vc=o) for the blend of the two linearenantiomeric polymers to a wave number 5 cm⁻¹ lower than that for theparent enantiomers. Likewise, a red shift of 7 cm⁻¹ was also observedfor the blend of the two cyclic enantiomers relative to the parentenantiomers. These results are consistent with the hypothesis that theblend forms a stereocomplex, sc-P(M1), assisted by the weak to moderateOC_(α)H—O=C hydrogen bonds.

Powder x-ray diffraction (XRD) profiles (FIG. 3D) of enantiomericl-P[(R)-M1] [(a) in FIG. 3D] and l-P[(S)-M1] (prepared using[M1]/[Y1]=1000/1), as well as their 1:1 l-P[(R)-M1]−l-P[(S)-M1] blend orsc-P(M1), all crystallized from CHCl₃, revealed substantially differentcrystalline diffraction patterns of the blend in comparison with theparent enantiomers. Chiefly, whereas the two enantiomeric polymersshowed identical patterns (consisting of four major diffraction signalsat 11.5°, 16.2°, 18.2°, and 20.6°, along with three minor peaks at 12.8,21.6°, and 25.2°), the blend exhibited a new, intense diffraction peakat 8.1° [d spacing (the spacing between adjacent planes)=1.1 nm] and wasalso devoid of the two signals (major, 11.5°, and minor,)12.8° presentin the enantiomers, which is attributable to the formation of thestereocomplex.

Although P[(R)-M1] or P[(S)-M1] is readily soluble in common polarorganic solvents such as CHCl₃, CH₂CL₂, and N,N′-dimethylformamide(DMF), sc-P(M1) is only partially soluble in CHCl₃ and insoluble inCH₂Cl₂, tetrahydrofuran, and DMF. Overall, the above corroborativeevidence showed that a nanocrystalline stereocomplex formed between thetwo enantiomeric P(M1) polymers and that such a stereocomplex exhibitedmarkedly enhanced crystallinity, crystallization rate, and solventresistance over those of the parent enantiomers.

In contrast, mixing of enantiomeric polymers P[(+)-4,5-T6GBL] andP[(−)-4,5-T6GBL] (Table 2) in a 1:1 stoichiometric ratio, followed bycrystallization, yielded a physical blend exhibiting thermal propertiesand spectroscopic characteristics essentially identical to those ofeither the starting enantiomeric polymer or the racemic polymerP[(±)-4,5-T6GBL]. DSC curves for the two enantiomeric polymers and theirphysical blend displayed the same features of an amorphous material,with a T_(g) of ˜72° C. FTIR spectra also revealed the same absorptionfeatures, with an identical vc=o stretching frequency of 1725 cm⁻¹observed for all of the three polymers (two enantiomeric polymers andtheir 1:1 blend).

Overall, the above collective evidence showed that no stereocomplexationoccurred upon mixing of these two enantiomeric polymers, and thus noenhancement of properties occurred through blending.

TABLE 2 Results of ROP of Chiral 4,5-T6GBL and Chiral 3,4-T6GBL (M1)Time Conv. M_(n) ^(c) M_(n,calcd) ^(d)

 ^(c) [α]_(D) ^(e) Run^(a) Monomer Cat. [M]/[cat.]/[I] (h) (%)^(b)(kg/mol) (kg/mol) (M_(w)/M_(n)) (°)  1 (−)-4,5- La1  500/1/3 40 38 10.99.08 1.06 71.2 T6GBL  2 (+)-4,5- La1  200/1/3 72 65 9.03 6.27 1.05 −70.9T6GBL  3 (R)-M1 Y1 1000/1 3 84 304 — 1.19 −100.2  4^(f) (R)-M1 Y1 1000/13 86 365 — 1.08 −100.3  5 (R)-M1 La1  500/1 3 82 40.1 — 1.38 −101.6  6(R)-M1 La1 1000/1/3 3 75 49.3 35.3 1.04 −99.4  7 (S)-M1 Y1 1000/1 3 88312 — 1.21 99.6  8^(f) (S)-M1 Y1 1000/1 3 85 260 — 1.15 100.3  9 (S)-M1La1  500/1 3 82 48.8 — 1.31 99.8 10 (S)-M1 La1 1000/1/3 3 78 35.8 36.61.06 100.3 ^(a)Conditions: 4,5-T6GBL = 210 mg in toluene (5.0M),3,4-T6GBL (M1) = 560 mg in neat, I = Ph₂CHCH₂OH, room temperature (~25°C.). ^(b)Determined by ¹H NMR in CDCl₃. ^(c)Number-average molecularweight (M_(n)) and dispersity index ( 

 = M_(w)/M_(n)) determined by gel-permeation chromatography (GPC) at 40°C. in CHCl₃ coupled with a DAWN HELEOS II multi (18)-angle lightscattering detector and an Optilab TrEX dRI detector for absolutemolecular weights. ^(d)Calculated based on: ([M]₀/[I]₀) × Conv. % ×(molecular weight of M1) + (molecular weight of I). ^(e)Specific opticalrotation, measured in chloroform at room temperature. ^(f)M1 = 12.0 g.

Mechanical and Rheological Properties

The thermomechanical properties of the amorphous polymer derived fromracemic M1 [rac-P(M1)] prepared with Y1 (M_(n)=875 kg/mol, Ð=1.07)(Table 1, run 19) and semicrystalline stereocomplex sc-P(M1) preparedwith Y1 (Table 2, runs 4 and 8) were examined by dynamic mechanicalanalysis (DMA) in a tension film mode. The thermomechanical spectra ofsc-P(M1) (FIG. 4A) and rac-P(M1) (FIG. 22) show that, at roomtemperature (the glassy state), both sc-P(M1) and rac-P(M1) exhibitedhigh storage modulus (E′) values, although E′ (1.58±0.44 GPa) ofsc-P(M1) was somewhat higher than that (1.47±0.25 GPa) of rac-P(M1).However, after the glass transition region with similar T_(g) values [83to 90° C., as defined by the peak maxima of tan δ, the lossmodulus/storage modulus ratio (E″/E′)] (FIG. 23), E′ of rac-P(M1)dropped by more than three orders of magnitude and then quickly went tothe viscous flow state. In contrast, E′ of sc-P(M1) decreased only byapproximately one order of magnitude after T_(g), and the material stillmaintained a high E′ in the rubbery plateau until reaching a flowtemperature of ˜180° C., characteristic of a semicrystalline materialhaving a high T_(m) (186° C. by DSC).

Tensile testing of dog-bone-shaped specimens of rac-P(M1) and sc-P(M1)yielded stress-strain curves (FIG. 4B), revealing that semicrystallinesc-P(M1) exhibited a much higher ultimate tensile strength(σ_(B)=54.7±4.0 MPa) and Young's modulus (E=2.72±0.25 GPa) thanamorphous rac-P(M1) (σ_(B)=26.2±3.2 MPa, E=1.85±0.30 GPa). As a glassymaterial, sc-P(M1) displayed an elongation at break (ε_(B)=6.5±1.2%),and the ε_(B) value for rac-P(M1) was approximately doubled, withε_(B)=13.1±3.5%. Overall, the key thermal and mechanical properties ofthe crystalline P(M1) (T_(g)˜50° C., T_(m)˜188° C., T_(d)˜340° C.;σ_(B)˜55 MPa, E˜2.7 GPa, ε_(B)˜7%) compare well to those of typicalcrystalline P(L-LA) materials (T_(g)˜54° to 59° C., T_(m)˜159° to 178°C., T_(d)˜235° to 255° C.; σ_(B)˜28 to 50 MPa, E˜1.2 to 3.0 GPa, ε_(B)˜2to 6%).

The angular frequency (ω) dependencies of the dynamic storage or elasticmodulus (G′) and loss or viscous modulus (G″) of rac-P(M1) and sc-P(M1)were characterized at six different temperatures (165°, 175°, 185°,195°, 205°, and 215° C.) in the linear viscoelastic regime (1.0% strain)established by the strain sweeps at 215° C. The data obtained fromfrequency sweep experiments at each temperature were compiled togenerate a master curve reported as a time-temperature superpositioncurve at reference temperature 215° C. [FIG. 4C for rac-P(M1)]. A G′ andG″ crossover point where G′ becomes larger than G″, indicating thetransition from the terminal (viscous) to the rubbery (elastic) region,was seen for both rac-P(M1) and sc-P(M1). The crossover frequenciesmeasured at 165°, 175°, 185°, 195°, 205°, and 215° C. for rac-P(M1) werefound to be 0.43, 0.75, 1.21, 1.95, 3.18, and 4.89 Hz, corresponding torelaxation times of 2.32, 1.33, 0.83, 0.51, 0.31, and 0.21 s,respectively.

The crossover frequencies observed for sc-P(M1) were more than six timeshigher at each of the same temperatures, thus giving rise to muchshorter relaxation times, from 0.34 s (165° C.) to 0.03 s (215° C.). Forthe high-molecular weight rac-P(M1) (M_(n)875 kg/mol), the meltprocessability was preliminarily tested by examining the dynamic meltviscosity as a function of the shear rate measured at 215° C. (FIG. 4D),showing that shear thinning started to develop at a low shear rate of˜0.1 s⁻¹ and became pronounced at ˜1 s⁻¹.

In conclusion, this work introduces a solution to three key challengesfacing the development of chemically recyclable polymers: selectivity indepolymerization, trade-offs between polymers' depolymerizability andtheir properties and performance, and a circular monomer-polymer-monomercycle. The results showed that, with judiciously designed monomer andpolymer structures, it is possible to create chemically recyclablepolymers that exhibit quantitative recyclability and useful materialsproperties and that the polymer synthesis and recycling processes can beperformed under ambient or industrially relevant conditions.

General Methods for Ring-opening Polymerization

Monomers: Two classes of ring-fused GBL monomers with trans-fusing offive, six, and seven-membered rings to the GBL ring at 3,4-(α,β) and4,5-(or β,γ)-positions (Scheme 1). Note that these structures alsoinclude their respective enantiomers and they can exist in racemic formsas well. In addition, monomers with a four-membered ring fused to theGBL ring are also possible. Furthermore, trans-disubstituted GBLderivatives represent an extreme ring-fused structure when the fusedring is very large. These types of trans-fusing to the parent GBL ringincrease the ring strain of GBL, thus rending such monomers readilypolymerizable, even under ambient conditions (room temperature, 1 atm).

Polymers: Upon polymerization, these two classes of ring-fused GBLmonomers can lead to either linear or cyclic polymers structures, orboth, depending the catalysts/initiators used and reaction conditionsemployed (Scheme 2). The resulting polyesters exhibit high thermalstability, with degradation temperature typically above 300° C., andhigh molecular weight up to 390 kg/mol; they can also be selectivelyrecycled back to monomers under heating and/or catalytic conditions.Also uniquely, enantiomeric polymers derived from enantiomeric monomers(R,R)/(S,S)-3 ,4-T6GBL can cocrystallize, via stereomatching and/orintermolecular interactions such as dipole-dipole interaction and weakinterchain C═O—H₂C—O hydrogen bonding, to construct a crystallinestereocomplexed sumpramolecular polymer with high melting-transitiontemperature (T_(m)), Scheme 3. It is anticipated that other3,4-ring-fused GBL and 4,5-ring-fused GBL enantiomeric monomers couldalso lead to similar stereocomplexed polymers. Copolymers can also beproduced by copolymerizing one such ring-fused GBL monomer with another,or such a ring-fused GBL with other common lactones such the parent GBL,β-butyrolactone, δ-valerolactone, ε-caprolactone, lactide, glycolide,etc.

Polymerization Processes: The ROP is typically carried out undersolvent-free conditions (i.e., bulk polymerization), or in solution(e.g., in toluene), at room temperature in the presence of catalyst.Suitable ROP catalysts can also be grouped into four classes: lanthanide(also referred to as rare-earth metal), transition-metal, main-group,and organic catalysts (Scheme 4). They can be used alone but can also beemployed in combination with a protic initiator such as alcohol.

Lanthanide (Ln) catalysts includef-block metal homoleptic andheteroleptic amides, alkoxide and alkyl complexes such as Ln(NR₂)₃,Ln(OR)₃, LnR₃, Ln(NR₂)_(x)(OR)_(3-x)(x=1, 2), or discrete LLn-Xcomplexes [L=dianionic ligand, bridged or unbridged, polydentate organicligands such as a tetradentate amino-alkoxy-bis(phenoxy); X═OR, NR₂, SR,R, where R is alkyl, aryl, substituted alkyl, or substituted aryl].Transition-metal catalysts include d-block metal discrete molecularcomplexes carrying at least one labile ligand, L_(n)M-X (X═OR, NR₂, SR,R), where R is alkyl, aryl, substituted alkyl, or substituted aryl,which complexes can either directly initiate the polymerization or reactwith an initiator to generate an active species. The metal center istypically protected by one or more bulky mono-dentate or polydentateorganic ligands such as a tetradentate amino-alkoxy-bis(phenoxy) ligand.Main-group catalysts include s- and p-block metal (groups 1, 2, 12, and13) metal homoleptic and heteroleptic complexes such as RLi, MgR₂, LM-X(M=Mg, Zn, X=R, OR, SR, NR₂), Al(OR)₃, and L₂AlOR, where R is alkyl,aryl, substituted alkyl, or substituted aryl.

Organic catalysts are those strong organic bases or nucleophiles, suchas triazabicyclodecene (TBD), that can either directly initiate thepolymerization or activate a protic initiator to promote thepolymerization. Basic catalysts can be grouped into two general classes:strong organic bases and inorganic bases. They can be used alone but areoften used in combination with a protic initiator. Organic catalystsinclude strong organic bases, especially polyaminophosphazene superbasessuch as1-tent-butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris(dimethylamino)-phosphoranylidenamino]-2λ⁵,4λ⁵-catenadi(phosphazene)(^(t)Bu-P₄); guanidines such as 1,5,7-triazabicyclo[4.4.0]dec-5-ene(TBD), proazaphosphatranes (cyclic azaphosphines), and cyclopropeniminesuperbases, including the following catalysts. Anonic versions oforganic catalysts/initiators such as urea or thiourea anions can also beused.

Inorganic bases include strong bases of alkaline and alkaline earthcompounds such as ROM (R=Me, Et, ^(i)Pr, ^(n)Bu, ^(t)Bu; M=K, Na, Li),(RO)₂M (R=Me, Et, ^(i)Pr, ^(n)Bu, ^(t)Bu; M=Mg or Ca), MH (M=K, Na, Li),MOH (M=K, Na, Li), and R₂NM (R=alkyl; M=K, Na, Li) wherein R is alkyl,aryl, substituted alkyl, or substituted aryl.

The above catalysts for polymerization and other compounds can also beused as catalysts for depolymerization to recover the monomer back.

Typical initiators include protic compounds such as alcohols (ROH),di-alcohols (HO—R—OH), polyols (compounds containing more than two OHgroups, or sugars; amines (RNH₂, R₂NH); thiols (RSH), where R is alkyl,aryl, substituted alkyl, or substituted aryl, or deprotonated monomers.

Summary

The development of chemically recyclable polymers offers a solution tothe end-of-use issue of polymeric materials and provides a closed-loopapproach toward a circular materials economy. However, polymers that canbe easily and selectively depolymerized back to monomers typicallyrequire low-temperature polymerization methods and also lack physicalproperties and mechanical strengths required for practical uses. Weintroduce a polymer system based on γ-butyrolactone (GBL) with atrans-ring fusion at the α and β positions. Such trans-ring fusionrenders the commonly considered as nonpolymerizable GBL ring readilypolymerizable at room temperature under solvent-free conditions to yielda high-molecular weight polymer. The polymer has enhancedthermostability and can be repeatedly and quantitatively recycled backto its monomer by thermolysis or chemolysis. Mixing of the twoenantiomers of the polymer generates a highly crystalline supramolecularstereocomplex.

General Synthetic Methods for Synthesis of Monomers

The invention also relates to methods of making the compounds andcompositions of the invention. The compounds and compositions can beprepared by any of the applicable techniques of organic synthesis, forexample, the techniques described herein. Many such techniques are wellknown in the art. However, many of the known techniques are elaboratedin Compendium of Organic Synthetic Methods (John Wiley & Sons, NewYork), Vol. 1, Ian T. Harrison and Shuyen Harrison, 1971; Vol. 2, Ian T.Harrison and Shuyen Harrison, 1974; Vol. 3, Louis S. Hegedus and LeroyWade, 1977; Vol. 4, Leroy G. Wade, Jr., 1980; Vol. 5, Leroy G. Wade,Jr., 1984; and Vol. 6, Michael B. Smith; as well as standard organicreference texts such as March's Advanced Organic Chemistry: Reactions,Mechanisms, and Structure, 5^(th) Ed. by M. B. Smith and J. March (JohnWiley & Sons, New York, 2001), Comprehensive Organic Synthesis;Selectivity, Strategy & Efficiency in Modern Organic Chemistry, in 9Volumes, Barry M. Trost, Ed.-in-Chief (Pergamon Press, New York, 1993printing)); Advanced Organic Chemistry, Part B: Reactions and Synthesis,Second Edition, Cary and Sundberg (1983); Protecting Groups in OrganicSynthesis, Second Edition, Greene, T. W., and Wutz, P. G. M., John Wiley& Sons, New York; and Comprehensive Organic Transformations, Larock, R.C., Second Edition, John Wiley & Sons, New York (1999).

A number of exemplary methods for the preparation of the compounds ofthe invention are provided below. These methods are intended toillustrate the nature of such preparations are not intended to limit thescope of applicable methods.

Generally, the reaction conditions such as temperature, reaction time,solvents, work-up procedures, and the like, will be those common in theart for the particular reaction to be performed. The cited referencematerial, together with material cited therein, contains detaileddescriptions of such conditions. Typically, the temperatures will be−100° C. to 200° C., solvents will be aprotic or protic depending on theconditions required, and reaction times will be 1 minute to 10 days.Work-up typically consists of quenching any unreacted reagents followedby partition between a water/organic layer system (extraction) andseparation of the layer containing the product.

Oxidation and reduction reactions are typically carried out attemperatures near room temperature (about 20° C.), although for metalhydride reductions frequently the temperature is reduced to 0° C. to-100° C. Heating can also be used when appropriate. Solvents aretypically aprotic for reductions and may be either protic or aprotic foroxidations. Reaction times are adjusted to achieve desired conversions.

Condensation reactions are typically carried out at temperatures nearroom temperature, although for non-equilibrating, kinetically controlledcondensations reduced temperatures (0° C. to −100° C.) are also common.Solvents can be either protic (common in equilibrating reactions) oraprotic (common in kinetically controlled reactions). Standard synthetictechniques such as azeotropic removal of reaction by-products and use ofanhydrous reaction conditions (e.g. inert gas environments) are commonin the art and will be applied when applicable.

Protecting Groups. The term “protecting group” refers to any groupwhich, for example, when bound to a hydroxy or other heteroatom preventsundesired reactions from occurring at this group and which can beremoved by conventional chemical or enzymatic steps to reestablish thehydroxyl group. Suitable hydroxyl protecting groups are known to thoseskilled in the art and disclosed in more detail in T. W. Greene,Protecting Groups In Organic Synthesis; Wiley: New York, 1981 (“Greene”)and the references cited therein, and Kocienski, Philip J.; ProtectingGroups (Georg Thieme Verlag Stuttgart, New York, 1994), both of whichare incorporated herein by reference.

The following Examples are intended to illustrate the above inventionand should not be construed as to narrow its scope. One skilled in theart will readily recognize that the Examples suggest many other ways inwhich the invention could be practiced. It should be understood thatnumerous variations and modifications may be made while remaining withinthe scope of the invention.

EXAMPLES Example 1 Synthesis of Monomers Materials and Methods

All syntheses and manipulations of air- and moisture-sensitive materialswere carried out in flamed Schlenk-type glassware on a dual-manifoldSchlenk line, on a high-vacuum line, or in an inert gas (Ar orN₂)-filled glovebox. High-performance liquid chromatography (HPLC)-gradeorganic solvents were first sparged extensively with nitrogen duringfilling 20 L solvent reservoirs and then dried by passage throughactivated alumina (for diethyl ether, tetrahydrofuran, anddichloromethane) followed by passage through Q-5 supported coppercatalyst (for toluene and hexanes) stainless steel columns. HPLC-gradeN,N-dimethylformamide (DMF) was degassed and dried over CaH₂ overnight,followed by vacuum distillation (CaH₂ was removed before distillation).Toluene-d₈ was dried over sodium/potassium alloy and vacuum-distilled orfiltered, whereas CD₂Cl₂ and CDCl₃ were distilled over CaH₂ and thenstored over activated Davison 4 Å molecular sieves.

All monomers were dried over CaH2 overnight, vacuum distillated, andstored over activated Davison 4 A molecular sieves in the glovebox forfurther use. tri[N,N-bis(trimethylsilyl)amide] lanthanum(III)La[N(SiMe₃)₂]₃ (La1) was purchased from Aldrich Chemical Co. and used asreceived. 1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD),2,2-diphenylethanol, diphenylmethanol and triphenylmethanol werepurchased from Aldrich Chemical Co., which were purified by dissolvingin toluene over CaH₂, filtering after stirring overnight, and removingthe solvent. Benzyl alcohol and 1, 8-diazabicyclo[5.4.0]undec-7-ene(DBU) were purchased from Fisher Scientific Co. and Aldrich Chemical Co.respectively, which were purified by distillation over CaH2 and storedover activated Davison 4 Å molecular sieves. Tetradentateamino-bisphenolate yttrium alkyl complex (Y1) and2,6-diisopropylphenylsubstituted β-diiminate zinc isopropoxide complex[(BDI)ZnO^(i)Pr] (Zn1) were prepared according to available procedures(Scheme 5).

Absolute Molecular Weight Measurements

Measurements of polymer absolute weight-average molecular weight(M_(w)), number-average molecular weight (M_(n)), and molecular weightdistributions or dispersity indices (Ð=M_(w)/M_(n)) were performed viagel-permeation chromatography (GPC). The GPC instrument consisted of anAgilent HPLC system equipped with one guard column and two PLgel 5 μmmixed-C gel permeation columns and coupled with a Wyatt DAWN HELEOS IImulti (18)-angle light scattering detector and a Wyatt Optilab TrEX dRIdetector; the analysis was performed at 40° C. using chloroform as theeluent at a flow rate of 1.0 mL/min, using Wyatt ASTRA 7.1.2 molecularweight characterization software. The refractive index increments(dn/dc) of the linear and cyclic P(M1) were determined to be0.0764±0.0014 mL/g and 0.0814±0.0030 mL/g, respectively, obtained bybatch experiments using Wyatt Optilab TrEX dRI detector and calculatedusing ASTRA software.

Polymer solutions were prepared in chloroform and injected into dRIdetector by Harvard Apparatus pump 11 at a flow rate of 0.25 mL/min. Aseries of known concentrations were injected and the change inrefractive index was measured to obtain a plot of change in refractiveindex versus change in concentration ranging from 0.4 to 2.0 mg/mL. Theslope from a linear fitting of the data was the do/dc of the polymer.

Selected linear and cyclic polymers, l-P(M1) and c-P(M1) produced byLa1/ROH and La1, respectively, were also analyzed by a Malvern Viscotek305 Triple Detector (light scattering, refractive index, and viscometer)Array GPC instrument equipped with a guard column and two PLgel 5 μmmixed-C columns (PL1110-6500, Agilent); the analysis was carried out at40° C. and a flow rate of 0.8 mL/min, with chloroform as the eluent, andthe chromatograms were processed with Malvern OmniSEC software (version4.7).

Spectroscopic Characterizations

The isolated low molecular weight samples were analyzed bymatrix-assisted laser desorption/ionization time-of-flight massspectroscopy (MALDI-TOF MS); the experiment was performed on anUltraflex MALDI-TOF mass spectrometer (Bruker Daltonics) operated inpositive ion, reflector mode using a Nd:YAG laser at 355 nm and 25 kVaccelerating voltage. A thin layer of a 1% NaI solution was firstdeposited on the target plate, followed by 0.6 μl of both sample andmatrix (DHB, 20 mg/mL in MeOH, 10% AAC). External calibration was doneusing a peptide calibration mixture (4 to 6 peptides) on a spot adjacentto the sample. The raw data was processed in the FlexAnalysis software(version 2.4, Bruker Daltonics).

X-ray powder patterns of the polymers were obtained with a ThermoScintag X-2 Powder X-Ray Diffractometer with Cu radiation (scan of2θ=5-30° with a step size of 0.02° and count time of 2 sec/step). Beforeanalysis, specimens were cooled by liquid N₂ and grinded until a finewhite powder was obtained.

Fourier transform infrared (FT-IR) spectroscopy was performed on aThermoscientific (Nicolet iS50) FT-IR spectrometer equipped with adiamond attenuated total reflectance (ATR) at room temperature in therange of 550-4000 cm⁻¹.

NMR spectra were recorded on a Varian Inova 400 MHz (FT 400 MHz, ¹H; 100MHz, ¹³C) or a 500 MHz spectrometer. Chemical shifts for all spectrawere referenced to internal solvent resonances and were reported asparts per million relative to SiMe₄.

Amorphous atactic P(M1) from racemic (±)-M1. ¹H NMR (CDCl₃, 25° C.):δ3.99-3.85 (m, 2H), 2.22-2.12 (m, 1H), 1.99-1.88 (m, 2H), 1.84-1.69 (m,3H), 1.49-1.40 (m, 1H), 1.33-1.02 (m, 3H). ¹³C NMR (CDCl₃, 25° C.):175.0, 174.9(4), 174.9(0), 174.8(7) (C═O), 67.1, 67.0 (O—CH₂), 46.0,45.8, 45.7, 45.6 (CHC═O), 38.2, 38.1(4), 38.1(0), (CHCHC═O), 29.8(cyclohexyl), 28.6, 28.5 (cyclohexyl), 25.2 (cyclohexyl), 25.0, 24.9(cyclohexyl).

Stereoregular (isotactic) P[(R)-M1)] from (R)-M1. ¹H NMR (CDCl₃, 25°C.): δ3.98 (dd, J=8.0, 4.0 Hz, 1H), 3.87 (dd, J=12.0, 8.0 Hz, 1H),2.18-2.12 (m, 1H), 2.01-1.91 (m, 2H), 1.84-1.69 (m, 3H), 1.50-1.41 (m,1H), 1.33-1.18 (m, 2H), 1.11-1.02 (m, 1H). ¹³C NMR (CDCl₃, 25° C.):174.9, 67.1, 46.0, 38.2, 29.8, 28.6, 25.2, 25.0.

Thermal, Mechanical, and Rheological Analysis

Melting-transition temperature (T_(m)) and glass-transition temperature(T_(g)) of purified and thoroughly dried polymer samples were measuredby differential scanning calorimetry (DSC) on an Auto Q20, TAInstrument. All T_(m) and T_(g) values were obtained from a second scanafter the thermal history was removed from the first scan. The secondheating rate was 10° C./min and cooling rate was 10° C./min.Decomposition onset temperatures (T_(onset)) and maximum ratedecomposition temperatures (T_(max)) of the polymers were measured bythermal gravimetric analysis (TGA) on a Q50 TGA Analyzer, TA Instrument.Polymer samples were heated from ambient temperatures to 700° C. at aheating rate of 10° C./min. Values of T_(max) were obtained fromderivative (wt %/° C.) vs. temperature (° C.), while T_(onset) values(initial and end temperatures) were obtained from wt % vs. temperature(° C.) plots.

Film specimens suitable for dynamic mechanical analysis (DMA) wereprepared via solvent-casting of concentrated polymer solutions inchloroform at 30-50° C. The sc-P(M1) films were afforded by combiningthe isolated (R)- and (S)-chiral polymer materials P[(R)-M1] andP[(S)-M1] in solution and stirred to generate the stereocomplex. Therac-P(M1) solutions were solvated directly for casting. Polymersolutions were solvent-cast using a syringe into PTFE molds and left todry gradually at room temperature in open air. Upon slow solventevaporation of chloroform, typically after 24-72 h, the films wereextensively dried overnight in a vacuum oven up to 100° C. and stored atroom temperature prior to analysis.

Storage modulus (E′), loss modulus (E″), and tan δ (E″/E′) were measuredby DMA on a Q800 DMA Analyzer (TA Instruments) in a tension film mode ata maximum strain of 0.05% and a frequency of 1 Hz (complying withstrain-sweep and frequency-sweep linearity analysis performed prior tosample testing). Specimens for analysis were generated viasolvent-casting of polymer materials in chloroform into PTFE molds(approx. 35×15×1.5 mm), dried, and cut down to a standard width (13 mm).Specimen length (5-10 mm) and thickness (0.10-0.30 mm) were measured fornormalization of data by Q-series measurement software (TA Instruments).Test specimens were mounted to screw-tight grips (maximum 2 N). Thesamples were heated from −50° C. to 250° C. at a heating rate of 3° C.min⁻¹. Glass transition temperature (T_(g)) was calculated as the peakmaxima of the tan δ curve. Samples were tested to the point of yield(amplitude of displacement >20 mm) with measurements repeated for 3specimens, the values reported are averaged from the measured data.

Tensile stress/strain testing was performed by an Instron 4442 universaltesting system (50 N load cell) on dog-bone-shaped test specimens (ASTMD638 standard; Type V) prepared via slow-solvent evaporation.Concentrated polymer and stereocomplex solutions in chloroform weresolvent cast into PTFE molds (approx. 73×54×7 mm), thoroughly dried, andcut using an ASTM D638-5-IMP cutting die (Qualitest) to standarddimensions. Thickness (0.10-0.40 mm) and grip length (25-26 mm) weremeasured for normalization of data by the Bluehill measurement software(Instron). Test specimens were affixed into the pneumatic grip (maximum2 kN) frame at 30 psi (N₂). Tensile stress and strain were measured tothe point of material break at a grip extension speed of 5.0 mm/min atroom temperature, with the measurements repeated for 4-6 specimens andthe values reported are averaged from the measured data.

For rheological analysis, isolated polymer materials rac-P(M1) andsc-P(M1) were compression-molded using a Carver Bench Top LaboratoryPress (Model 4386) equipped with a two-column hydraulic unit (Carver,Model 3912, maximum force 24000 psi). Materials were loaded betweennon-stick Teflon paper sheets into a steel tile mold with insetdimensions 50×50×2 mm (Carver, Model 818701D) and compressed between two6″×6″ steel electrically heated platens (EHP) at clamp force 5000 psi,temperature 200-205° C. for five minutes.

Rheological measurements were performed on a Discovery Series HR-2hybrid rheometer (TA Instruments) under nitrogen gas flow (30 psi). Testspecimens were loaded between two 8 mm steel electrically heated platen(EHP) loading discs. Test specimens were trimmed at a temperature of215° C. with measurements performed at gap lengths 500±10 μm and anexperimental axial force of 0.15±0.05 N. The linear viscoelastic regionof the materials was first determined by a percent strain (γ)oscillating amplitude sweep (strain 8.0×10⁻⁵-100%, 215° C.). Oscillatingfrequency sweeps were then performed in a logarithmic fashion (5 pointsper decade) within the linear viscoelastic region (1.0% strain) from 0.1to 100 and 500 rad s⁻¹ under continuous direct oscillation and apre-analysis soak time of 5 min to allow for specimen thermostatization.The frequency sweep measurements were performed at 165, 175, 185, 195,205, and 215° C. and the data compiled to a master curve reported as atime-temperature superposition curve at reference temperature 215° C.

Monomer Preparations

Preparation of 3,4-T6GBL (M1):

To a stirring suspension of NaBH4 (5 g, 129.7 mmol) in THF (100 mL) at0° C. was added dropwise trans-1,2-cyclohexanecarboxylic acid anhydride(10 g, 64.8 mmol) in THF (30 mL). The mixture was allowed to stir atroom temperature for 5 h. The reaction solution was cooled to 0° C. andquenched by the addition of 4 M HCl (80 mL) and diluted with water (100mL). The mixture was extracted with Et₂O (3×200 mL). The combinedorganic layers were washed with brine and dried over anhydrous Na₂SO₄,filtrated, and concentrated in vacuo. The crude products were used forthe next step directly.

To a solution of crude products in 300 mL of benzene was addedpara-toluenesulfonic acid (0.5%). The reaction mixture was heated toreflux with azeotropic removal of water, using a Dean Stark trap. After12 h, the reaction mixture was cooled to room temperature andconcentrated in vacuo. The resultant residue was purified by flashchromatography (1:5 EtOAc/hexanes) to afford 3,4-T6GBL (8.3 g, 91% fortwo steps). The spectral data correlates with the previously reporteddata for 3,4-T6GBL. ¹H NMR (400 MHz, CDCl₃): δ4.35 (dd, J=8.4 and 6.4,1H), 3.85 (dd, J=10.8 and 8.4, 1H), 2.16-2.14 (m, 1H), 2.02-1.83 (m,5H), 1.34-1.22 (m, 4H).

Preparation of (R)-3,4-T6GBL [(R)-M1]:

A suspension of (1R, 2R)-cyclohexane-1,2-dicarboxylic acid (5.0 g, 29mmol) in acetic anhydride (15 mL) was heated to 80° C. for 1 h. Thereaction solution was cooled to room temperature and concentrated invacuo. The product was pure enough for the next step directly. To astirring suspension of NaBH₄ (2.5 g, 66.1 mmol) in THF (50 mL) at 0° C.was added dropwise (3aR, 7aR)-hexahydroisobenzofuran-1,3-dione (4.47 g,29 mmol) in THF (20 mL). The mixture was allowed to stir at roomtemperature for 7 h. The reaction solution was cooled to 0° C. andquenched by addition of 4.0 M HCl (10 mL) and diluted with water (20mL). The mixture was extracted with Et₂O (3×100 mL). The combinedorganic layers were washed with brine and dried over anhydrous Na₂SO₄,filtrated, and concentrated in vacuo. The crude products were useddirectly for the next step directly.

To a solution of the above crude products in 200 mL of benzene was addedpara-toluenesulfonic acid (0.5%). The reaction mixture was heated toreflux with azeotropic removal of water, using a Dean Stark trap. After12 h, the reaction mixture was cooled to room temperature andconcentrated in vacuo. The resultant residue was purified by flashchromatography (1:5 EtOAc/hexanes) to afford (R)-3,4-T6GBL (3.5 g, 86%for three steps). [α]_(D) ²⁶=36.1° (c=0.5286 g/100 mL, CHCl₃). ¹H NMR(400 MHz, CDCl₃): δ4.35 (dd, J=8.4 and 6.4, 1H), 3.85 (dd, J=10.8 and8.4, 1H), 2.16-2.14 (m, 1H), 2.02-1.83 (m, 5H), 1.34-1.22 (m, 4H).

Preparation of (S)-3,4-T6GBL [(S)-M1]:

A suspension of (1S, 2S)-cyclohexane-1,2-dicarboxylic acid (5.0 g, 29mmol) in acetic anhydride (15 mL) was heated to 80° C. for 1 h. Thereaction solution was cooled to room temperature and concentrated invacuo. The product was pure enough for the next step directly. To astirring suspension of NaBH₄ (2.5 g, 66.1 mmol) in THF (50 mL) at 0° C.was added dropwise (3aS, 7aS)-hexahydroisobenzofuran-1,3-dione (4.47 g,29 mmol) in THF (20 mL). The mixture was allowed to stir at roomtemperature for 7 h. The reaction solution was cooled to 0° C. andquenched by addition of 4 M HCl (10 mL) and diluted with water (20 mL).The mixture was extracted with Et₂O (3×100 mL). The combined organiclayers were washed with brine and dried over anhydrous Na₂SO₄,filtrated, and concentrated in vacuo. The crude products were useddirectly for the next step directly.

To a solution of the above crude products in 200 mL of benzene was addedpara-toluenesulfonic acid (0.5%). The reaction mixture was heated toreflux with azeotropic removal of water, using a Dean Stark trap. After12 h, the reaction mixture was cooled to room temperature andconcentrated in vacuo. The resultant residue was purified by flashchromatography (1:5 EtOAc/hexanes) to afford (S)-3,4-T6GBL (3.66 g, 90%for three steps). [α]_(d) ²⁶=−36.3° (c=0.4074 g/100 mL, CHCl₃). ¹H NMR(400 MHz, CDCl₃): δ4.35 (dd, J=8.4 and 6.4, 1H), 3.85 (dd, J=10.8 and8.4, 1H), 2.16-2.14 (m, 1H), 2.02-1.83 (m, 5H), 1.34-1.22 (m, 4H).

Preparation of 4,5-T6GBL:

To a solution of NaH (5.8 g, 240 mmol) in 150 mL of THF was addedacetonitrile (14.6 mL, 280 mmol). A solution of cyclohexene oxide (19.8g, 200 mmol) in 50 mL of THF was added to the reaction mixture bysyringe. The reaction mixture was heated to 65° C. for 24 h and thencooled to 0° C. The reaction mixture was treated with water andconcentrated in vacuo. The remaining solution was extracted with 5×200mL of Et₂O, the combined organic layers were washed with 100 mL ofsaturated aqueous NH₄Cl, 100 mL of aqueous 0.1 M H₂SO₄ and 200 mL ofbrine, then dried over anhydrous Na₂SO₄, filtrated, and concentrated invacuo. The residue was purified by flash column chromatography(Hexanes/EtOAc=3/1) to give compound S1 (65% yield) as colorless oil. ¹HNMR (400 MHz, CDCl₃): δ3.37-3.30 (m, 1H), 2.64 (dd, J=16.8 and 4.0, 1H),2.50 (dd, J=16.8 and 7.6, 1H), 2.04-1.98 (m, 1H), 1.93-1.91 (m, 1H),1.80-1.72 (m, 2H), 1.60-1.52 (m, 2H), 1.34-1.20 (m, 4H).

To a solution of NaOH (60 g, 1.5 mol) in 300 mL of a 2:1 mixture ofethanol:water was added S1 (20 g, 143.7 mmol). The reaction mixture washeated to reflux for 24 h and then cooled to 0° C. The reaction mixturewas treated with dilute HCl to adjust the PH˜7 and concentrated invacuo. The remaining solution was extracted with 4×200 mL of Et₂O. Thecombined organic layers were washed with 200 mL of brine and dried overanhydrous Na₂SO₄, filtrated, and concentrated in vacuo. The residue waspure enough to use for the next step directly. ¹H NMR (400 MHz, CDCl₃):δ3.27 (dt, J=10.0 and 4.4, 1H), 2.71 (dd, J=15.6 and 6.0, 1H), 2.45 (dd,J=15.6 and 6.4, 1H), 2.02-1.99 (m, 1H), 1.84-1.73 (m, 3H), 1.67-1.65(m,1H), 1.31-1.21 (m, 3H), 1.13-1.06 (m, 1H).

To a solution of acid S2 (22.7 g, 143.7 mmol) in 300 mL of benzene wasadded para-toluenesulfonic acid (0.5%). The reaction mixture was heatedto reflux with azeotropic removal of water, using a Dean Stark trap.After 12 h, the reaction mixture was cooled to room temperatrue andconcentrated in vacuo. The resultant residue was purified by flashchromatography (10:90 EtOAc/hexanes) to afford 4,5-T6GBL (19.3 g, 95%).¹H NMR (400 MHz, CDCl₃): δ3.77 (dt, J=10.4 and 3.2, 1H), 2.49 (dd,J=16.4 and 6.4, 1H), 2.24-2.17 (m, 2H), 1.96-1.84 (m, 3H), 1.79-1.76 (m,1H), 1.52 (dq, J=11.2 and 3.2, 1H), 1.45-1.22 (m, 3H).

Preparation of (−)-4,5-T6GBL and (+)-4,5-T6GBL:

A stirred solution of rac-4,5-T6GBL (10.0 g, 71.3 mmol) and(R)-1-(-naphthyl)-ethylamine (12.2 g, 71.3 mmol) in xylene (50 mL) washeated at reflux under N₂ for 39 h. The solvent was concentrated and thediastereomeric amides were separated completely by flash columnchromatography (hexanes/EtOAc=1/1) to give the high-R_(f) amide-a as anoff-white solid. ¹H NMR (400 MHz, acetone-d₆): δ8.19 (d, J=8.4 Hz, 1H),7.92 (d, J=8.0 Hz, 1H), 7.82 (d, J=8.0 Hz, 1H), 7.62-7.45 (m, 5H),5.94-5.87 (m, 1H), 4.19-4.16 (m, 1H), 3.16-3.11 (m, 1H), 2.63 (dd,J=14.4, 5.2 Hz, 1H), 2.08-2.03 (m, 1H), 1.90-1.86 (m, 1H), 1.80-1.76 (m,1H), 1.70-1.55 (m, 6H), 1.29-0.97 (m, 4H). ¹H NMR (400 MHz, acetone-d₆)for the low-R_(f) diastereomer amide-b (also an off-white solid): δ8.19(d, J=8.0 Hz, 1H), 7.92 (d, J=8.4 Hz, 1H), 7.81 (d, J=8.4 Hz, 1H),7.62-7.45 (m, 5H), 5.94-5.87 (m, 1H), 4.19 (d, J=3.6 Hz, 1H), 3.15-3.07(m, 1H), 2.67 (dd, J=10.4, 2.8 Hz, 1H), 2.06-2.01 (m, 1H), 1.89-1.86 (m,1H), 1.73-1.51 (m, 7H), 1.29-0.90 (m, 4H).

To a solution of NaOH (4.0 g, 10 mol) in 40 mL of a 3:1 mixture ofethanol:water was added amide-a (1.6 g, 5.1 mmol). The reaction mixturewas heated to 110° C. for 48 h and then cooled to 0° C. The reactionmixture was treated with dilute HCl to adjust the PH ˜7 and concentratedin vacuo. The remaining solution was extracted with 4×200 mL of Et₂O.The combined organic layers were washed with 200 mL of brine and driedover anhydrous Na₂SO₄, filtrated, and concentrated in vacuo. The residuewas purified by flash column chromatography (hexanes/EtOAc=1/1) to giveacid-a (0.72 g, 89% yield) as an off-white solid. ¹ H NMR (400 MHz,CDCl₃): δ6.50 (brs, 2H), 3.27 (dt, J=10.0, 4.4 Hz, 1H), 2.71 (dd,J=15.6, 6.0 Hz, 1H), 2.45 (dd, J=15.6, 6.4 Hz, 1H), 2.02-1.99 (m, 1H),1.84-1.73 (m, 3H), 1.67-1.65 (m,1H), 1.31-1.21 (m, 3H), 1.13-1.06 (m,1H).

To a solution of acid-a (0.72 g, 4.55 mmol) in 30 mL of benzene wasadded para-toluenesulfonic acid (0.5%). The reaction mixture was heatedto reflux with azeotropic removal of water, using a Dean Stark trap.After 2 h, the reaction mixture was cooled to room temperature andconcentrated in vacuo. The resultant residue was purified by flashchromatography (10:90 EtOAc/hexanes) to afford (−)-4,5-T6GBL (0.63 g,98%) as an off-white solid. The spectral data correlate with thepreviously reported data for (−)-4,5-T6GBL (56). [α]_(D) ^(24.4)=−84.2°(_(c)=0.1916 _(g)/100 mL, CHCl₃). ¹ H NMR (400 MHz, CDCl₃): δ3.77 (dt,J=10.4, 3.2 Hz, 1H), 2.49 (dd, J=16.4, 6.4 Hz, 1H), 2.24-2.17 (m, 2H),1.96-1.84 (m, 3H), 1.79-1.76 (m, 1H), 1.52 (dq, J=11.2, 3.2 Hz, 1H),1.45-1.22 (m, 3H).

To a solution of NaOH (4.0 g, 10 mol) in 40 mL of a 3:1 mixture ofethanol:water was added amide-b (1.6 g, 5.1 mmol). The reaction mixturewas heated to 110° C. for 48 h and then cooled to 0° C. The reactionmixture was treated with dilute HCl to adjust the PH ˜7 and concentratedin vacuo. The remaining solution was extracted with 4×200 mL of Et₂O.The combined organic layers were washed with 200 mL of brine and driedover anhydrous Na₂SO₄, filtrated, and concentrated in vacuo. The residuewas purified by flash column chromatography (hexanes/EtOAc=1/1) to giveacid-b (0.68 g, 85% yield) as an off-white solid. ¹H NMR (400 MHz,CDCl₃): δ6.50 (brs, 2H), 3.27 (dt, J=10.0, 4.4 Hz, 1H), 2.71 (dd,J=15.6, 6.0 Hz, 1H), 2.45 (dd, J=15.6, 6.4 Hz, 1H), 2.02-1.99 (m, 1H),1.84-1.73 (m, 3H), 1.67-1.65 (m,1H), 1.31-1.21 (m, 3H), 1.13-1.06 (m,1H).

To a solution of acid-b (0.68 g, 4.55 mmol) in 30 mL of benzene wasadded para-toluenesulfonic acid (0.5%). The reaction mixture was heatedto reflux with azeotropic removal of water, using a Dean Stark trap.After 2 h, the reaction mixture was cooled to room temperature andconcentrated in vacuo. The resultant residue was purified by flashchromatography (10:90 EtOAc/hexanes) to afford (+)-4,5-T6GBL (0.59 g,98%) as an off-white solid. The spectral data correlate with thepreviously reported data for (+)-4,5-T6GBL (56). [α]_(D) ^(24.4)=+84.6°(c=0.1980 g/100 mL, CHCl₃). ¹H NMR (400 MHz, CDCl₃): δ3.77 (dt, J=10.4,3.2 Hz, 1H), 2.49 (dd, J=16.4, 6.4 Hz, 1H), 2.24-2.17 (m, 2H), 1.96-1.84(m, 3H), 1.79-1.76 (m, 1H), 1.52 (dq, J=11.2, 3.2 Hz, 1H), 1.45-1.22 (m,3H).

Preparation of substituted bicyclic monomers or bridgehead containingmonomers were prepared in general by the examples shown in Scheme 7.

Example 2 Thermodynamic Studies

In a glovebox under an argon atmosphere, an NMR tube was charged with Y1(7.4 mg, 9.8 μmol), and 0.3 mL of toluene-d₈. The NMR tube was sealedwith a Precision Seal rubber septum cap and taken out of the gloveboxand immersed in a cooling bath at −78° C. After equilibration at −78° C.for 10 min, M1 (68.7 mg, 0.49 mmol, [M1]/[Y1]=50/1) in toluene-d₈ (0.4mL) was added via a gastight syringe and the NMR tube was brought into a500 MHz NMR probe precooled to the desired polymerization temperature(−25, −30, −35 and −40° C., respectively). The conversion of the monomerwas monitored by ¹ H NMR at different time intervals until theconversion remained constant at each temperature. Worth noting here isthat the isomerization to the non-polymerizable cis-isomer was less than3% under the low temperatures.

The equilibrium monomer concentration, [M1]_(eq), obtained by plotting[M1] as a function time until the monomer concentration reached aconstant, was measured to be 0.4154, 0.3316, 0.2679, and 0.2248 M for−25° C., −30° C., −35° C., and −40° C., respectively. The Van't Hoffplot of ln[M1]_(eq) vs. 1/T gave a straight line with a slope of −2.37and an intercept of 8.67, from which thermodynamic parameters werecalculated to be ΔH°_(p)=−20 kJ·mol⁻¹ and ΔS°_(p)=−72 J·mol⁻¹·K⁻¹, basedon the equation ln[M1]_(eq)=ΔH_(p)/RT−ΔS°_(p)/R (22). The ceilingtemperature was calculated T_(c)=−11, 0, 62, or 88° C. at [M1]₀=0.7 M,1.0 M, 5.0 M, or 8.2 M (bulk), respectively, based on the equationT_(c)=ΔH°_(p)/(ΔS°_(p)+Rln[M1]₀).

Example 3 General Polymerization Procedures

Polymerizations were performed in 5 mL glass reactors inside theglovebox for ambient temperature (˜25° C.) runs, or in 25 mL Schlenkflasks interfaced to a dual-manifold Schlenk line with an externaltemperature bath for runs at other temperatures. In a typicalpolymerization reaction, catalyst was added to the vigorously stirredmonomer. After a desired period of time, the polymerization was quenchedby addition of 3 mL HCCl₃ acidified with HCl (5%). The quenched mixturewas precipitated into 100 mL of cold methanol, filtered, washed withmethanol to remove any unreacted monomer, and dried in a vacuum oven at50° C. to a constant weight (see Table 3 and FIGS. 5-12).

Example 4 General Stereocomplexation Procedures

Stereocomplexes were prepared from a mixture of isotactic (R)-polymerand (5)-polymer in a 1:1 molar ratio (approximately 300 mg total). Thesolid polymer sample was dissolved in CHCl₃ (20 mg mL⁻¹), filteredthrough a plastic frit (0.45 μm pore size nylon filter), and allowed toevaporate slowly and undisturbed for 3-7 days. The obtained crystallinesolid was collected and dried in a vacuum oven at 60° C. to a constantweight.

Example 5 Thermal Recycling of P(3,4-T6GBL)

A sealed tube containing 40 mg of the purified P(3,4-T6GBL) sample (freeof catalyst residue) under an argon atmosphere was heated at 300° C.(for the linear polymer) for 1 h or at 300° C. (for the cyclic polymer)for 24 h. After cooling, a colorless liquid was formed and confirmed tobe the cleanly and quantitatively recycled monomer 3,4-T6GBL by ¹H NMRanalysis (see FIGS. 19 and 20).

Example 6 Chemical Recycling Procedures

A sealed tube containing 40 mg of the purified P(M1) sample (free ofcatalyst residue) under an argon atmosphere was heated at ≥300° C. for 1h (for the linear polymer) or for 24 h (for the cyclic polymer). Aftercooling back to room temperature, a colorless liquid was formed andconfirmed to be the cleanly and quantitatively recycled monomer M1 by ¹HNMR analysis. The experiment was repeated at the gram scale and the sameresult was obtained by gravimetric and ¹H NMR analysis.

TABLE 3 Selected Results of ROP of 4,5-T6GBL^(a) [0.56 g, except run 7,2.80 g), initiator (I) = Ph₂CHCH₂OH, ~25° C.]. Time ConversionM_(n(exptl)) ^(b) M_(n(calcd)) ^(c) I*

^( b) un Catalyst [M1]/[Cat.]/[I] Solvent (h) (%)^(a) (kg mol⁻¹) (kgmol⁻¹) (%)^(d) (M_(w)/M_(n))  1 La1  100/1/3 neat 5 71 3.88 3.47 89 1.03 2 La1  200/1/3 neat 5 70 7.52 6.74 90 1.03  3 La1  200/1/2 neat 5 6910.7 9.87 92 1.04  4 La1  200/1/1 neat 5 38 11.4 10.8 95 1.29  5 La1 500/1/3 neat 8 64 14.8 15.2 103 1.01  6 La1 1000/1/3 neat 8 53 20.124.9 124 1.01  7 La1 1000/1/3 neat 23 58 29.2 27.3 94 1.01  8 La12000/1/3 neat 24 30 30.2 28.2 93 1.02  9 La1  200/1/0 neat 18 32 19.1 —— 1.25 10 La1  200/1/0 toluene (5.0M) 18 45 21.0 — — 1.14 11 La1 200/1/0 toluene (5.0M) 24 56 20.8 — — 1.21 12 La1  500/1/0 toluene(5.0M) 24 29 33.1 — — 1.12 13 La1 1000/1/0 toluene (5.0M) 24 17 32.2 — —1.14 14 Y1  500/1/0 neat 10 53 47.2 37.2 79 1.07 ^(a)Monomer conversiondetermined by ¹H NMR in CDCl₃. ^(b)M_(n) and  

 values determined by GPC at 40° C. in CHCl₃ coupled with a DAWN HELEOSII multi (18)-angle light scattering detector and an Optilab TrEX dRIdetector for absolute molecular weights. ^(c)Calculated based on:([M]₀/[I]₀) × Conv. % × (molecular weight of monomer) + (molecularweight of I). ^(d)Initiation efficiency (I*) = M_(n) (calcd)/M_(n)(exptl) × 100.

ZnCl₂ Catalyzed Depolymerization of P(3, 4-T6GBL).

The chemical recycling experiment was also performed in the presence ofa simple Lewis acid catalyst. In a glovebox under argon atmosphere, a 25mL tube was charged with purified P(3,4-T6GBL) (56 mg), ZnCl₂ (2%) andtoluene (1 mL). The reactor was sealed, taken out of the glovebox, andimmersed in the oil bath. The mixture was stirred at 120° C. (for thelinear polymer) for 12 h or at 120° C. (for the cyclic polymer) for 24h, after which the reaction mixture was concentrated to give a colorlessliquid, which was confirmed to be the cleanly recycled monomer 3,4-T6GBLby ¹H NMR analysis (see FIGS. 21 and 22).

Polymerization-depolymerization cycles in a multi-gram scale. Pure M1(7.00 g) was first polymerized by Znl according to the above describedpolymerization procedures, and the resulting P(M1) was isolated andpurified. In a glovebox under argon atmosphere, a 25 mL flask wascharged with the purified P(M1), ZnCl₂ (2 mol%). The reactor was sealed,taken out of the glovebox, and connected to a vacuum-distillation uniton a Schlenk line under N₂. The mixture was stirred at 180° C. undervacuum (0.01 Torr) to collect a colorless liquid on the receiver, whichwas confirmed to be the cleanly recycled monomer M1 by ¹H NMR analysis.The recovered monomer was repolymerized directly without furtherpurification by Zn1 to reform P(M1). The flowchart below (Scheme 6) thattracked the mass balance of the polymer product and recovered monomerfor chemical recycling of P(M1), showing essentially quantitativerecovery of the pure monomer after each of threepolymerization-depolymerization cycles.

Example 7 Synthesis of Block and Random Copolymers

Diblock copolymer of 4,5-T6GBL with ε-caprolactone (ε-CL) wassuccessfully synthesized by sequential addition of the monomers.Specifically, 4,5-T6GBL was polymerized first in toluene using a[4,5-T6GBL]/[La1]/[ROH] ratio of 200/1/3, at which point an aliquot waswithdrawn to obtain monomer conversion (46% by ¹h NMR) and M_(n) (5.52kg/mol, Ð=1.04 by GPC) values. Next, 100 equivalents of ε-CL (relativeto Lal) were added and polymerized for 10 min, at which point 99%conversion of ε-CL was achieved while no further conversion of 4,5-T6GBLwas observed. GPC analysis of the resulting copolymer showed a single,unimodal peak, which was shifted to a higher molecular weight region nowwith M_(n)=10.8 kg/mol and Ð=1.17, indicating successful formation ofdiblock copolymer P(4,5-T6GBL)-b-PCL. The large reactivity differencesbetween 4,5-T6GBL and ε-CL ensured that the ROP of 4,5-T6GBL did notoccur concomitantly in the ROP step of ε-CL step. The molar compositionof the diblock copolymer (57 mol % ε-CL) measured by ¹H NMR was close tothe calculated ratio (56 mol % ε-CL) based on the monomer conversiondata. The well-defined diblock copolymer structure was also confirmed by¹H NMR analysis, which showed the presence of only two types of carbonylresonances attributed to homo-sequences of ε-CL and 4,5-T6GBL units ofcopolymer P(4,5-T6GBL)-b-PCL. The thermal property of the diblockcopolymer was analyzed by differential scanning calorimetry (DSC) andthermal gravimetric analysis (TGA). The second heating scan DSC curve ofP(4,5-T6GBL)-b-PCL (57 mol % ε-CL) showed only one melting-transitiontemperature (T_(m)) of 51° C., while the glass-transition temperature(T_(g)) typically at 72° C. attributed to homopolymer P(4,5-T6GBL) wasnot observed, which further demonstrated the diblock copolymerformation. TGA and DTG (derivative thermogravimetry) curves ofP(4,5-T6GBL)-b-PCL displayed two degradation steps; T_(d) (onsetdegradation temperature, defined by the temperature of 5% weight loss)of 318° C. and T_(max) (maximum degradation temperature, defined by thepeak value in DTG) of 352° C. and 407° C. correspond to the P(4,5-T6GBL)and PCL domains, respectively, which provided additional evidence forthe formation of the diblock copolymer from sequential blockpolymerization.

Example 8 Living Characteristics of Polymerization

In the ring-opening polymerization of 4,5-T6GBL byLa[N(SiMe₃)₂]₃]/[Ph₂CHCH₂OH], there exhibited linear increase of theresulting polyester molecular weight as a function of monomer conversionwhile maintaining low dispersity, thus showing living characteristics ofthis polymerization.

While specific embodiments have been described above with reference tothe disclosed embodiments and examples, such embodiments are onlyillustrative and do not limit the scope of the invention. Changes andmodifications can be made in accordance with ordinary skill in the artwithout departing from the invention in its broader aspects as definedin the following claims.

All publications, patents, and patent documents are incorporated byreference herein, as though individually incorporated by reference. Nolimitations inconsistent with this disclosure are to be understoodtherefrom. The invention has been described with reference to variousspecific and preferred embodiments and techniques. However, it should beunderstood that many variations and modifications may be made whileremaining within the spirit and scope of the invention.

What is claimed is:
 1. A polymer comprising Formula I, Formula II, orFormula III:

wherein Q and R are the terminal ends of the polymer, or Q and R takentogether form a cyclic polymer of Formula I, Formula II, or Formula III;G is O, S, or NR^(z); R^(x), R^(y) and R^(z) are each independently H or—(C₁-C₈)alkyl; m is about 20 to about 10⁶; and n is 1-20; wherein theR^(y) substituents have a trans-configuration relative to each other,each —(C₁-C₈)alkyl moiety is independently branched or unbranched, andeach ring-embedded carbon independently has an optional —(C₁-C₈)alkylsubstituent or phenyl substituent.
 2. The polymer of claim 1 wherein Gis O.
 3. The polymer of claim 1 wherein R^(x) is H, or R^(y) is H. 4.The polymer of claim 1 wherein Q is —(C₁-C₈)alkyl, N(R^(A))₂, OR^(A), orSR^(A), and R is H, wherein each R^(A) is independently H,—(C₁-C₈)alkyl, Ph₂CHCH₂—, or —Si[(C₁-C₈)alkyl]₃.
 5. The polymer of claim1 wherein the polymer has a number average molecular weight (M_(n)) ofabout 0.1 kg mol⁻¹ to about 5×10⁶ kg mol⁻¹, and/or the polymer has apolydispersity index of about 1 to about
 3. 6. The polymer of claim 1wherein the polymer is thermally depolymerizable or chemicallydepolymerizable to a monomer.
 7. The polymer of claim 6 wherein thermalor chemical depolymerization of the polymer provides about 95% orgreater conversion of the polymer to the monomer.
 8. A method forpolymerization comprising contacting a monomer with a catalyst and anoptional protic initiator to form a polymer via a ring openingpolymerization reaction of the monomer, wherein the monomer is a monomerof Formula IV or Formula V:

or an enantiomer or mixture thereof, wherein: G¹ is —C(═O)— and G² is O,S, or NR^(z); or G¹ is O, S, or NR^(z) and G² is —C(═O)—; G³ is O, S, orNR^(z); R^(x), R^(y) and R^(z) are each independently H or—(C₁-C₈)alkyl; and n is 0-20; wherein each —(C₁-C₈)alkyl moiety isindependently branched or unbranched, and each ring-embedded carbonindependently has an optional —(C₁-C₈)alkyl substituent or phenylsubstituent.
 9. The method of claim 8 comprising forming the polymer ata pressure of about 1 atm to about 10 atm and at a temperature of about0° C. to about 100° C.
 10. The method of claim 8 wherein the catalyst isa metal-based catalyst or an organic catalyst.
 11. The method of claim10 wherein the metal-based catalyst istris[N,N-bis(trimethylsilyl)amide]lanthanum(III),

wherein X is a donor solvent molecule.
 12. The method of claim 8 whereinthe protic initiator is an alcohol, a thiol, or an amine.
 13. The methodof claim 8 wherein the monomer is a monomer of Formula IVA or FormulaIVB:

or an enantiomer or mixture thereof, wherein n is 1-20.
 14. The methodof claim 8 wherein the monomer is a monomer of Formula IVC or FormulaIVD:

or an enantiomer or mixture thereof, wherein n is 1-20.
 15. The methodof claim 8 further comprising quenching the polymerization reaction toform a polymer.
 16. The method of claim 15 wherein the monomer is amonomer of Formula IVA:

or an enantiomer or mixture thereof, wherein n is 1-20; the catalystcomprises a nucleophile (Q); and the polyester is a polyester of FormulaVI:

wherein: Q is the nucleophile and R is H, or Q and R taken together forma cyclic polymer of Formula VI; and m is about 20 to about 10⁶.
 17. Themethod of claim 15 wherein the monomer is a monomer of Formula IVB:

or an enantiomer or mixture thereof, wherein n is 1-20; the catalystcomprises a nucleophile (Q); and the polyester is a polyester of FormulaVII:

wherein Q is the nucleophile and R is H, or Q and R taken together forma cyclic polymer of Formula VII; and m is about 20 to about 10⁶.
 18. Themethod of claim 8 wherein the method further comprises contacting thepolymerization reaction with a second monomer.
 19. The method of claim18 wherein the second monomer is a lactone or lactide.
 20. The method ofclaim 18 wherein a block or random copolymer is formed by contacting thepolymerization reaction with a second monomer.
 21. The method of claim16 wherein the polymer is recycled to the monomer by thermaldepolymerization or chemical depolymerization.
 22. The method of claim16 wherein stoichiometric amounts of a polyester having astereo-configuration formed from one enantiomer of the monomer, and asecond polyester having the opposite stereo-configuration formed fromthe other enantiomer of the monomer are co-crystallized to form acrystalline stereocomplex, wherein the crystalline stereocomplex has ahigher melting temperature than said polyester having thestereo-configuration or opposite stereo-configuration.